Refilling laptop batteries!

The Li-Ion battery in my IBM Thinkpad X31 laptop has been getting a bit long in the tooth. Rated at a 4.4 AH capacity new, /proc/acpi/battery/BAT0/info told me that it was only holding 1.8 AH now that it was a few years old. (This is normal for Li-Ion batteries, which degrade over time, even without multiple charge-discharge cycles.)

X31 laptop battery

 A brand new IBM (or Lenovo now) battery costs over a hundred dollars, but by shopping around I was able to find a "compatible" battery for as low as $50. It was only rated at 4.4AH, but that is relatively close to the 2nd generation 4.8AH batteries that IBM/Lenovo sell for twice as much. I started to wonder if it might be cheaper to buy  OEM li-ion cells and simply replace the cells (keeping the case, and charge/discharge electronics). The first step would be to determine what type of Li-Ion cells I'd need to buy, so I decided to open up my old battery.

X31 battery disassembled

As you can see, the standard X31 battery has six cells, in three parallel groups of 2. Cells are nominally 3.6volts, so this adds up to 3 x 3.6 or 10.8 volts. In the photo I have removed the shrink wrapped packaging from one cell to view the markings. Note the relatively complicated PCB along the back side of the cells that handles charging and discharging. If you zoom into the photo, you can see that the controller PCB is connected to each end of every pair of cells (orange and black wires to the far ends, silver metal tab connections to the middle two). This allows the controller to charge each parallel pair of cells at a different rate. The controller PCB is also connected to a thermocouple that is resting between the two middle cells. This gives the controller a temperature reading on the cells during charging and discharging. If the PCB detects that the temperature is too high, it can lower the charging rate, or shut down the power draw (and laptop).  Also note the heat fuse (small white block in series with the power line between the two leftmost cells) that is designed to open the circuit if the charge/discharge controller for some reason fails to maintain a safe temperature. All of these safeguards are designed to keep your laptop battery from igniting, and will be very important to maintain in any "re-manufactured" batteries.

I actually determined what type of li-ion cells were used by measuring them and then looking for li-ion cells of a similar size. They are about 2.5" high by 11/16" diameter, or very close to the 64.9mm x 18.3m diameter size of a 18650 style cell that I found on www.batteryspace.com.

My battery is rated at 4.4AH, or 4400mAH. As it has three sets of parallel cells, each set of two cells must have a 4400mAH capacity (because they are in series, you add the voltage, not the amperage), so each cell must have a 2200mAH capacity. 

From a mAH per dollar standpoint, batteryspace.com's 2000mAH cells are the best value, but I decided that since the total cost difference was only six dollars, I could afford purchasing the 2200mAH cells. These are slightly lower than the 2400 mAH capacity of the newcells that Ibm/Lenovo now use, and I'll end up with a 4.4AH battery (just like the original part number, before IBM/Lenovo upgraded it to 4.8AH).

Just the cells cost $34.20, but I chose to purchase them with solder tabs attached (an extra $1.50) because I figure the people at batteryspace.com are better than me at attaching tabs, plus having extra tabs to work with (those that come on the cells, plus those I salvage from the original cells) will make my life easier. (Besides, the $7 of shipping is the largest extra expense….if the 2600mAH cells weren't almost twice as expensive as the 2200mAH cells I'd have gotten them just get a 5.2AH capacity battery!) The total cost was $43.42. A week later my batteries arrived. (Thanks UPS!)

Important safety note!

You should never replace li-ion cells with cells that have a lower capacity rating, or charge/discharge rate rating. The electronics in laptop batteries are programmed to prevent the cells from overheating and catching fire, and do a very good job as long as the replacement cells in the battery are of equal or higher rating than the original cells. 

Batteries

240 thoughts on “Refilling laptop batteries!

  1. Lex,

    I was successful with refilling a “replacement” x31 battery, that was not manufactured by IBM/Lenovo. It is possible that “official” controllers will self destruct if you un-hook them from cells/power.

    Trying to hot-swap the cells without removing power to the controller at any point should work if you are able to do it successfully. (Indiana Jones music in the background…)
    Jay

  2. Hi Guys, Iv done a Repack for my Toshiba notebook (Battery pack: PA3479U) and I had the problem of not charging and the pack was not powering the machine at all, because I disconnected the controller board. What I did to “reinitialize” the controller to accept charge and power the machine was to manually discharge the pack to about 3.1v per cell with the controller connected. After doing that the pack started low level charging until the cells were with in spec of the controller to allow fast charge. Now the pack works 100% and I am quite happy with my handy work.

    P.S. I used lithium polymer cells and I now have 8800mah of battery from the old 4400mah:)

    Julz

  3. I have looked at a couple battery suppliers and the 18650 cells all seem to be rated at 3.7 volts now. I know I need three 3.6 volt cells to match my battery pack which has a 10.8 volt output. Will this work if I use 3 x 3.7 volt cells for a 11.1 volt battery output? Is my laptop going to blow up from this 0.3 difference in voltage?

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  6. Hi Jay

    I got a wierd situation here , HELP !!

    – Just opened the battery (GA-M912M netbook ) : P/N 92BT0020F.
    – I see 4xCGR18650CG [MH12210] cells (Panasonic) , rated at 2200 (avg). 3.6V.
    – 4×2200 = 8800mAh
    – But the Battery is rated 4500 !!!!
    4400 = half 8800. usually a manufacturer would rate at lower to be on the safe side…

    So what do I do now ? and how would you suggest I go about dis/connecting the new for the old ?

    and i forgot … it 7.2V (2×3.6V) 4500mAh .

    Thx a bunch for this page ! 2011 and still going .. 🙂

    • It sounds like they have 2 pairs of 2 cells. Each cell is wired in parallel with another, and then the two pairs are wired in series. This gives 7.2v total (2×3.6) but it also doubles the individual cell capacity (2200×2 = 4400). I expect that the battery is rated at 4500 because the 2200 rated cells actually give 2250mAH each, so 2250×2 = 4500 mAh.

      As long as you keep the connections exactly the same, you should be able to replace each cell with another 18650 style cell and have everything work.

      Depending upon the battery charging/discharging circuit….Some people have commented that you should never remove power from the circuit while replacing the cells. So, insert the new cell before removing the old cell. This makes it so that the battery management circuit doesn’t know that you’ve replaced the cells. This keeps it from shutting down…but many battery management circuits don’t care…that behavior varies from brand to brand…

  7. Hi, I opened up my thinkpad x61t 8 cell battery pack. This is made of two strings of 4 cells, total 8 cells. 4 are 18650, and the other four are rectangular ones. But I couldn’t find any rectangular cells anywhere(about 50x35x9, by eyeballing)

    Anyways, I decided to just replace the four cylindrical cells, which are 18650. I’m thinking of putting in 2600mah LG cells. Costs $38 including shipping. My current battery holds about 62% of original capacity, and I’ve done the calculations. If I replace only one string cylindrical cells and all goes well, I’ll still end up with 108% of original design capacity. Would it be worth it? I’m not too worried about only replacing one string because I think they are controlled separately from each other.

    One more question, to feed the voltage while replacing cells, I’m planning to use a voltage/current generator. Should I use 4.05V as each individual cells currently measure, and replace one cell at a time, or should I provide 16.20V for the entire string and swap the whole string at once? I’m thinking I need to do 4.05V, and replace the individual cell one by one, because they each have wire connection to the circuit board for individual measuring voltage.

    Another question, what current should I be using? 50mA?

    By the way, I read those ebay 3000 mah 4000 mah battery are bogus and they are junk.

    • As long as the two strings are able to “share” the load, replacing one of the two strings should still increase your battery life. I think you will need to provide power and replace cells one at a time. (Typically most battery management circuits have a small “sensor” wire that goes between each pair of cells, and you need to keep the proper voltage on that wire as well as the series “power” wires at the end.) I have no idea what current you need to provide. I expect that you would only need 50mA to trick the BMS chip into thinking the cell is still there, but it would not hurt to use the full rating of the max current that the cells can provide (as long as you don’t accidentally short your wires!)
      Jay

  8. hey,nice i’m planning on building, my battery is a 6cell and i’m having trouble finding the correct size, they are the same colour as the ones in the photos(or look the same) what model number are your replacement batteries?

  9. My cells are standard “18650” cells. You can buy them with various different mAh ratings. You probably want to pay extra for the largest you can find if you are going to go through the effort of replacing them. (Or perhaps buying one size smaller than the largest, as sometimes the largest capacity cells charge a premium.)

  10. Hello My Jay..
    I’ve 12 Cell Ultra Capacity Battery of HP… since a month back it is giving me trouble i.e. it is not charing more than 100%, just it stuck on 40% and then after few time stop on 44%…
    Now i already opened the Battery Case and found that there is some Samsung 2200mah batteries installed.
    I searched a lot on internet and found that i can get each battery at a cost of $6…… for the same 2200 MAh.. because the HP battery check make report that Battery Capacity = 6600 MAh… so i think that if i’ll go over this 2200 mah capacity i’ll not able to get proper working of the battery….
    also guide me that if there is any Flash chip installed in this battery so if there is any i can rather go to buy another 12 cell ultra battery instead of Cell replacemnt..

    Kindly update me on my email also..

    support@crestcomm.net

    Tauseef Masood

    • If you are going to replace the cells, you can either replace them with the exact same power level, or buy slightly more expensive cells to get more capacity. (I recommend spending a little more money to get slightly higher capacity cells. The amount of work is the same regardless of the capacity of the cells you buy, and it’s a good amount of work, so you may as well get as much benefit as you can out of it.)

      Even if the electronics think they have 2200 cells, if you substitute 2400 or 2500 or 2600 mAh cells you will probably find that you can make use of the extra capacity (even though the power control electronics may be slightly confused, and report that you are at 0% battery remaining for a half hour or so before the battery is fully used up). Charging it usually regulated by voltage and current draw, so it will charge up the cells fully, even if they are somewhat larger that it is expecting.

      Unfortunately, I am not familiar with that specific battery, so I do not know if the chip is programed to “die” when/if you remove the cells. The safe thing is to connect the new cells before removing the old cells (so the power electronics never “notice” that the cells were removed). This takes a bit of effort, but is the only way to be 100% sure that the replacement will be successful.
      Jay

  11. Thanks for your quick reply…

    How I can connect the new cells before removing old? Do u have any video or information to share?

    Any help will be batter…

    • My recommendation is to solder the new cells up in the same
      configuration as the old cells. Then, solder a wire from the new cells
      to the power control chip in all the appropriate places.

      (basically, the new cells and the old cells will be in parallel)

      Then, cut the wires that go to the old cells after the new cells are all
      hooked up. As far as the power control electronics know, the cells were
      never unhooked.

      Jay

  12. Dear Jay.

    I Live in a city where about 90 % percent poeple purchase usde loptop computers, which usually imported from European countries. there model also used to be out dated , in which the majorproblem comes with batteries, which literally do not provide sufficient back up. I have very much interest in this repairing work, and I want to learn it properly. therefore , I need your kind advice.
    If I start learning this repairing work, can I do? As I have no experince indeed in this work. And for the purpose what exact tools are required for my workshop?

    Looking forward for a positive response.

    mashalkhan28@yahoo.com

    • You can do it, but it will take some practice and learning before you get good at it. Also you should know that some batteries are not easily refillable due to their control electronics not accepting new cells.

      For tools you will need some screwdrivers, a plastic separation tool
      (plastic prybars, blade, dremel with saw blade, etc) plus a soldering
      iron. (Ideally you’d have a li-ion welding machine if you plan on doing
      this a lot, but they are more specialized.)

      Jay

  13. Hi Jay,
    just for the record-I have HP Compaq 610 and the new battery (2600mhz Samsung) works ok for 3.5 Hours !!
    (original works with 1 hour on full brightness).

    My problem is that the battery bar show 0% after only 12 minutes! and if I shutdown when batt on 0% the computer do not open again, just until I plugged it again.

    Maybe when the batt is on 0% the chip on the batt do not let the computer to start.

    I’ve tried to charge it to 100% and discharge it fully (in linux) so the computer shutdown in a moment with no hibernate, but it didn’t calibrate my batt.

    Now I don’t know what to do,when I want to use the computer I have to:
    1. charge it full.
    2. open on linux
    3. wait 10 minutes to discharge to 0%
    4. restart to win 7 and have about 3 hours of working on 0% with no time bar.

    Do you have another solution?

    Thanks!

    • It sounds like you have successfully replaced the cells, but the power management chip is not “learning” about the new capacity. When I replaced my cells I had to do full charge/discharge cycles 5-7 times, and my chip gradually learned about the new capacity. If your chip is set up so that it will only allow capacity to go down (and never “grow”) you will never be able to get a good capacity measure on your new battery. Hopefully you will be able to modify power settings in your OS so that the OS does not shut down automatically when the battery (falsely) reports a low reading.

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  15. if your system wont run on the battery or the battery wont charge after doing this it might not be the flash there are fuses on the motherboard that blow sometimes when you replace the batteries due to them being weak and after you do this they cant handle the full power…so replacing these have fixed the issue for several of the laptops that have been brought to me after they did this and thought they messed something up…they didn’t so i say check the fuses and rule out everything before thinking its a flash issue

  16. Its okay that we can change the cells of a laptop battery,
    but can we increase the number of cells in parallel to give long backup time with same output.
    eg:
    a battery of 6 cells with 11.1V at 4400mAh
    increased to 9 cells with 11.1V at 6600mah
    the output will be same but the work hour will be increased.
    I have a doubt that it will harm ma laptop…so please clear ma doubt…..i have Dell Inspiron N5010 Laptop

    • You should be able to add extra cells in parallel to accomplish exactly what you want (Extend the amount of time the battery can power your laptop.) It will take your laptop longer to charge up (as the electronics are going to limit the charging current as if it still has 6 cells instead of 9) but that actually means that you will be charging each cell slower than normal, so they won’t get quite as hot when charging. (They also won’t get as hot when discharging, because each cell is providing less power at any one point in time.)

  17. I do not bother about the charging time it takes to charge i can give as much as it will, jus i want is long backup so by doing this jus i want to confirm that the battery i am going to use or the laptop will not be damaged.

    • When opening a piece of electronic equipment and soldering extra things to it you always have the chance of damaging it, but unless you hook something up incorrectly I expect that it will work fine. Even if you mess things up, it is more likely that the battery will stop working than you will actually be able to harm your laptop. The biggest problem I see is how you will physically mount the extra cells to the battery so that you can still plug it into your laptop.

  18. Your project is very good I would like to use for my netbook s10-2 that after 2 years the battery is almost dead (when i bought it has 15% treadwear).
    The cells that is build with are samsung icr18650-22f, so I have to choose new 18650 cells with 2.2Ah?
    My other question is that the cells are not attached to each other and to the controller with wires but with flat metal (i don’t know how to describe it) and the problem is that I want to solder the new cells before removing the old ones (for the memory). Can I use any other simple wire???

    I will buy cells from an internet shop from China so I want to know how can I test the new cells that are not DOA

    Thank you!!!

    • You can use any 18650 cells that are 2200 mAh (or greater if you want more capacity). You could possibly even use cells of a smaller mAh rating, but they may be charged slightly too fast and heat up more than is recommended.

      Due to the amount of work involved, I recommend paying for the largest capacity cells you can buy that are not outrageously expensive. The flat metal “thick foil” is used because it is easy to weld to the batteries, can be folded to get the batteries very close together, and is inexpensive. You can use any wire as long as it is able to conduct the same amount of energy as the metal foil. (My old X10 laptop takes 10-13 watts of power from the battery, newer larger laptops may take more.)

      The only real good way to test cells is to charge them up with a voltage/current controlled power supply, then discharge them to make sure they have full capacity. This takes time and somewhat specialized equipment. In your case, as long as all of the cells have a similar voltage level when they arrive, they are probably good to go.

  19. Great, thanks guys,

    any advice How to know if flash chip is present on battery, would be very helpful.

    thanks again, looking forward for any explantion in regard to my question

    • You really won’t know if your batteries charging circuit will “die” if you unplug the cells until you try. If you have read reports of other people easily replacing cells in the same brand/model battery before yours is probably safe. If you have no idea, you may want to connect the new pack in parallel with the old pack and then disconnect the old pack. (When doing this, you want to watch out for the new pack overcharging the old pack when they are connected, so make sure you charge the old pack (or discharge the new pack) so their voltages are very similar.)

  20. Hi, very nice write up. I did this to my Vaio battery, but now it is not detected by my laptop at all. I think the circuit you were talking about is not allowing current from my batteries past it. I know the batteries are charged, I checked them. Thanks.

    • It does sound like perhaps the VIAO battery has a “self destruct” code that keeps it from working after it detects that the original cells have been removed.

    • You may be able to “reflash” or “reset” the chip, but I wouldn’t know how. You’ll have to do some / a lot of research about the specific battery charging control chip used in the circuit board on those batteries. That isn’t impossible, but unless somebody has already figured it out for that specific battery type, it will take a lot of work to figure out.

      For others doing cell replacement with your type of battery, it sounds like they should build up the “new” battery pack out of the new cells, then connect the whole thing “in parallel” with the existing (but very old) battery pack of “old” cells, and only then disconnect the old cells. (You’ll want to make sure that the new cells are charged to about the same voltage as the old cells so lots of current doesn’t flow one way or the other. The easiest way would be to charge all cells before connecting.) This way, the monitoring and control chips don’t notice the swapout.

      In my case, I actually replaced cells in a “generic” laptop battery, and apparently the generic battery manufacturer didn’t think it was critical to prevent people from replacing the cells. (Just like generic ink cartridges allow you to refill them…)

  21. What I’ve found so far is that the negative battery side is getting all the way to the main negative pin. The positive side is not allowed to pass to the positive pin. I soldered in a wire directly from the pos. batt. side to the pos. pin and it did actually power my laptop, however my laptop still didn’t detect the battery therefore was unable to charge it. So that wouldn’t work. What I really need to find on this battery is a pin out diagram. No luck so far.

  22. Hi, Jay
    This is Ramesh, I need some information from you.
    I am having HP HDX16 note book since one year without no problem. Usually my computer getting heat in normal use, and when i am working with video editing , it will get more heat, but I never considered that heat because of I checked my processor graph as 99 percent when in editing mode. Recently battery stopped working suddenly, but its showing as 29% available and plugged in charging, but when I removed power card computer getting off. why?

    My question is what was problem with battery?
    Why computer is not using remaining 29% power?
    Gradually decreasing power in the battery to 27,26,25% why its not charging?
    I like to replace the cells is it possible?
    I cant able find cells in our country market, can I use any LI.3.6 cells from other brand battery or same HP DV4 battery(my battery model same like as DV4battery model) 10.8v, 55w
    If I want to replace how to check cells condition, can you give me some guidelines in the refilling the battery

    Thank you
    Ramesh

    • It is possible that a thermal cut-off switch inside of your battery has tripped (due to the overheating when video editing).

      I don’t think that this indicates a problem with your individual cells, so replacing them may not fix the problem. First thing to try is to remove the battery from the laptop, and turn the laptop off, and let them both cool off overnight. Hopefully the thermal switch will re-set (and it’s not a fuse that is blown forever). If it never re-sets, you may need to purchase a new battery.

  23. Thanks Jay for this nice tutorial. After reading this I decided to give a try on my laptop’s battery, which has been dead for 3 years.

    My laptop is Mitac8640M4 model. Which looks very similar to winbook laptops. The battery pack is made of by Panasonic, model CGR-B/T19SE-MSL (14.8V – 6000mAh).

    There is no battery indicator on task bar, but in power option properties it shows a red cross mark on a battery and 0%. When I remove the battery pack it shows not present.

    All I want to know is that, is the circuitry still working or not (3+ years not working)? Can I use over 6000mAh cells like 6600mAh or 7500mAh cells or lithium polymer pack?

    Waiting for your expert opinion.

  24. Thanks Jay for this nice tutorial. After reading this I decided to give a try on my laptop’s battery, which has been dead for 3 years.

    My laptop is Mitac8640M4 model. Which looks very similar to winbook laptops. The battery pack is made of by Panasonic, model CGR-B/T19SE-MSL (14.8V – 6000mAh).

    There is no battery indicator on task bar, but in power option properties it shows a red cross mark on a battery and 0%. When I remove the battery pack it shows not present.

    All I want to know is that, is the circuitry still working or not? Can I use over 6000mAh cells like 6600mAh or 7500mAh cells or lithium polymer pack?

    Waiting for your expert opinion.

    • It sounds like your battery charging circuit is still working (and talking with the laptop) as the display changes from “bad cells in the battery” to “no battery” when you remove it. You should be able to replace the 6AH cells with 6.6 or 7.5AH cells without problems, although charging will take a slightly longer amount of time (but discharging should also last longer as well ;>). If your battery protection circuit is designed to “shut itself down” if the cells are removed, you may want to solder the old cells in parallel with the new cells, before disconnecting the old cells. This way the battery protection circuit may not know that you have made the swap.

  25. Hi Jay

    Thanks for your reply. Once again I need your advice. I’m having hard time finding right kind of battery cells. I was searching the net for 6.6 or 7.5 AH cells. Though I find some but don’t know what would be the right voltage for me. Because there are no voltage sign on the battery cells. So, how to determine what is the right voltage for me. As the battery pack says (14.8V – 6000mAh). I have 12 cells altogether in my battery pack.

    • All battery cells of the same chemistry have the same voltage, so typically websites don’t bother listing the voltage. If you have 12 cells overall, and the battery pack is labeled as 14.8 volts and 6000 mAh, it sounds like you have 4 sets of 2 cells in parallel. LiIon cells are typically around 3.2-3.7 volts (nominal, they go higher when fully charged and lower when fully discharged). So a set of 4 cells in series is 14.8 volts. Because you have sets of 2 in parallel, each cell is actually only half the Ah capacity, or 3000 mAh. So you are looking to replace them with 3000 mAh (or 3Ah) cells (or similar…)

  26. Just replaced a Thinkpad T400 6-cell battery and it is totally not worth it. Don’t know if it works yet, will plug it in later, but the problem is first, the case now doesn’t shut completely, the front of the batter doesn’t (other side of the connector). Replacing the cells was a nightmare, there was only one short 2-inch wire and everything else was the flexible sheet that is soldered to the battery that wouldn’t come off. I don’t think its worth it, yes if the battery works, I will try to get at least 2 years out of it, will probably use black duck tape to keep the case completely closed.

    • Yes, it is definitely a lot more work/time/value than just buying a replacement battery. If you are good with the assembly you can make everything fit, but unless you know the BMS control board inside allows cell replacement you have no guarantee that it will work until you try it out.

  27. I think the either the plastic has changed or the design has changed in such a way that putting them together is a lot harder now. I don’t there was any way of taking the case apart without destroying some of the plastic there is required to snap the case back together. I will find out later today if it works.

  28. Looks like the battery is dead, won’t charge at all. I have the Thinkpad T400, I wonder if the battery died when I took the cells off. Well probably did, I know I soldered the batteries correctly, though there are more wires than usual.
    Any suggesting, besides checking if the wiring is good. Is there to check if the electronics stopped working when I took the batteries off line.

    • If your battery is “stock” IBM/Lenovo the BMS electronics inside are likely to turn off if any of the cells are removed. (Some people have reported that by soldering the new batteries in place before removing the old batteries they have successfully handled the “hand-off” without disabling the built in BMS board. However, if you do this you have to be sure that the old cells and new cells are very close to the same voltage so that not too much current flows between them when you connect them.)

      If you have a generic replacement battery, the BMS boards are less likely to shut off just because the cells are removed as part of a replacement.

      Before you give up on it, leave it in your laptop for a few days, rebooting and/or shutting off your laptop for a few hours every day/overnight, it is possible it will reset itself.

  29. Hi Jay,

    I replaced my battery cell on my laptop dell D 610. All look great , my battery lasts more than 2 hours, only the timer gets confused, and the charging flash light in my laptop blinks in red; no matter charging or when is fully charged, it doesn’t stop. I can’t understand what’s wrong? Any advice from you. thanx again

    • Glad it’s (mostly) working for you. I suspect that either your laptop’s BIOS or your battery’s BMS board need to re-calibrate itself. If you are lucky, going through a few full charge/discharge cycles will eventually do this. (If you are unlucky, they do not have a re-calibration scheme, and only go in one direction (down) and now can’t understand why your battery is lasting so much longer than it used to.) Try turning your laptop completely off, removing the battery, pressing the power button for a few seconds, and then putting the battery back in to see if that re-sets anything.

  30. I had no luck changing the cells in the Thinkpad T400 battery. Thus, I have 6 New LG Lithium 18650 Rechargeable Cells (3.7V 2600mAh), never used. Anyone in Chicago is willing to buy them. I received them in June.

  31. im trying to make a battery pack for my homemade speakers but i cant find a safety circuit that i could buy so i thought that i could use the circuit in the battery but i cant find the pins that are positive and negative and i still want to be able to charge the battery’s. The battery’s are from a old Sony vaio laptop.

    • Hi John,

      You might want to check out BatterySpace.com for a selection of battery management systems:
      http://www.batteryspace.com/pcbbmscmbfordiy.aspx
      Pick the correct voltage for the number of cells you have. For a set of speakers, I don’t expect that the Amperage will be much higher than 500 mA or perhaps 1000 ma (same as 1 amp) if they are really big speakers. If your speakers have a power jack, they may also have a sticker that tells what their current draw is.

  32. the battery’s are SANYO li-ion 3.7v with a capacity of 1900 MAH. the thing is that i dont live in the us and i don’t want to order something outside my country and the speaker is just on medium sized speaker wit a small 5W apm that runs on 9-14vDC. so i need to know if i can use the circuit that comes with the battery pack or what would happen if i use the battery’s and charge them without the circuit.

    • You could wire 3 cells in series (11.1 volts) to power your speakers. With only a 5 watt draw, they will never overheat your cells. The only danger is that if you leave them on they will completely drain the cells to 0 volts, which will kill them, but not in a spectacuarly burning way…just a slow death that won’t hurt anything but the cells. As long as you charge them before they get too low they will be fine.

      The bigger danger is overcharging your cells. If you can find a regulated power supply that puts out exactly 11 or 11.1 volts and never goes higher, that would charge them safely (assuming that 3.7 volts is the correct charging voltage on a per-cell basis, some cells have lower charging voltages and some have higher ( up to 4.2 volts). As long as you are monitoring the voltage levels and remove the batteries when they are changed you can use just about anything to charge them, the harder bit is to find something that won’t overcharge them when left unattended.

  33. ok now you seam to know about this stuff so what kind of battery do you recommend i want the battery to be longlasting. do you recommend using the li-ion, a 12V 1,5-2AH lead acid battery or jsut some regular rechargeable AA battery’s.

    thank you!

    • 1900 mAh li-ion batteries are basically 1.9 mAh batteries. Three (or four) of them would be close to equivalent to a “12 volt” battery (which typically ranges from 11-13 volts in actual usage, and higher when being charged. A 5 watt draw at 12 volts is 0.41 amps, which is 25% of the total 2 Ah capacity. The LiIon batteries would actually run this load for longer (closer to 4 hours) than the lead Acid battery (which has a 2 Ah Capacity, but only if discharged over 20 hours….not 4 hours…) They would also weigh less. The advantage of the 12 volt battery is that it won’t burst into flames (as easily) if you overcharge it, and you can find 12 volt lead acid battery chargers all over the place.

      Regular rechargeable AA’s are typically NiMH chemistry, which is somewhere between Lead Acid and Li-Ion in capacity. AA battery chargers are also dead easy to find.

      If you are looking for easy to purchase and charge, rechargeable AA batteries are hard to beat. Since you already have LiIon cells, they would make the best choice if you can find a way to charge them safely.

  34. ok thank you for everything it was very helpfull!

    but i want to know how you calculated how long the lifetime was so that i maybe could use it to get some batteries that would last even longer

    • The actual “lifetime” that a battery can drive a load depends upon the AH rating of the battery, and the rate at which you are discharging it, plus the battery chemistry, using something called the Peukert Number which is based upon the chemistry (and sometimes, brand) of the battery.
      See:
      http://www.csgnetwork.com/batterylifecalc.html

      The easy way to get more life is to buy a battery with more AH rating. All things being equal, LiIon is better than NiMH, which is better than Lead Acid in most applications (except for ease of charging).

  35. If my laptop is plugged in 95% of the time. How do you setup the battery management to make the battery last the longest?

    • Don’t start charging your battery until it is down to 70% capacity (30% discharged), and only charge it until it reaches 80% capacity. (Most laptops will fully charge the battery, assuming you want as much capacity as possible, so you may need to set things up to “not charge until 70%” and then manually unplug the battery once it reaches 80% to stop charging, then put it back in, or charge it to 100%, and then discharge it manually to 80%.

  36. Hi Jay,

    I tried following your advice; by turning the laptop off, removing the battery and than restarting again and putting back the battery but no luck at this time.
    I can’t understand, power meter shows o time left and my comp continue to work about one hour more, but the flash light continue to blink 4-5 times red and one time green. This does every time I insert the battery in my laptop. Strange ha?

    many thanks again

    • I ran into a problem like this with my laptop after refilling the battery. The BMS board didn’t “know” that the cells had been replaced, so assumed that they had the same (reduced) capacity of the old cells. This meant that the BMS board told the laptop’s power meter that the battery was essentially empty (zero on the power meter). BUT, since the cells could continue to provide power for a lot longer, the laptop would run for an extra hour or so…..

      For me, my BMS was eventually smart enough to figure out that the cells had “recovered” and it re-set it’s “capacity available” numbers. It did take 5-10 charge cycles. If your BMS is not as smart, it may never reset it’s capacity available number.

    • If you run your laptop until the battery is actually empty, the laptop will shut down immediately due to loss of power. If your operating system is in the middle of writing something to disk when this happens, the file system may get corrupted. This could lead to having to run a chkdisk like program, or a completely corrupted hard drive (at very worst case scenario) that would require a re-format and re-install.

  37. thanks Jay for you valued advises.
    I will keep using same battery and see if anything changes.
    I am wondering if I can replace NI -CD element with LI-Io cells that have PCB for a power tool. Is it safe. Can PCB of each cell protect the battery from overheating?

    Do I have to remove PCB from each cell when I use them to replace to one old computer battery that has charging control circuit or should I use them with PCB. Does charging control circuit and PCB of each battery element conflict each other? Thx and Have a great day

    • I’m not 100% sure that I understand your question. You should NEVER use a BMS PCB from a LiIon cell on a NiMH cell (or visa versa). However, if you have a LiIon pack of cells that is protected by a BMS system (and it provides the same voltage as a NiMH pack of cells) you should be able to replace the NiMH pack with the LiIon pack. If the pack is wildly undersized, it will overheat and the BMS system should shut it down, either by detecting the excessive current draw, or because the temperature sensor in the cells has triggered.

  38. My apologize for a messy question.

    1. can I replace Ni Cd batteries with Li-Io in batteries (with PCB) in a power tool. (of course the same voltage and higher mah)

    2. If want to replace cells to laptop battery, and I am using li-io cells with PCB, do I have to remove the PCB from each cell before I use them and put them in laptop battery pack?
    Thank you again very much,

    • 1. Yes, you should be able to do this with no major problems. If the capacity of the battery pack is much greater, you may want to watch out for the motor on the tool overheating if you run it longer than it was designed for. Of course, you will have to use an appropriate LiIon charger, instead of the standard NiMH charger.

      2. If you are replacing laptop LiIon cells, you should be able to re-use the existing circuit board. (So of the cells came with their own circuit board you can discard it). Some BMS systems will “die” and refuse to work if you disconnect them from power from a battery, so some people have “hot swapped” cells (soldering in the new cells before disconnecting the old cells). You must be careful that both the new and old cells have the same voltage so they don’t transfer too much current back and forth before the old cells are removed.

  39. i have laptop hp 6910p i want change the cells.my battry is 4400 mali ampaire i want make him 1200mah .each cell 3500mah and 6 cell make how to mah. battry voltage 10.6

    • It sounds like your current battery has 6 2200 mAh cells in a 2 parallel 3 series arrangement. (2200 X 2 = 4400) (3 X 3.5volts = 10.6 volts)

      If you replace your 2200 mAh cells with 3500 mAh cells, you will have a 3500 X 2 = 7000 mAh battery at 10.6 volts. The total capacity of your battery will be 2600 mAh larger.

  40. Thanks Jay,

    Relating to question 2 that I mentioned earlier, I guess I can’t discard the existing circuit board of the battery but i have to remove the circuit board of each cell? Do I? Hope I got it right?

    thanks a lot, it really helps

    • If each of your new/replacement cells has it’s own circuit board then it sounds like they have their own fuse/BMS built in that is different from a “whole battery” BMS that most laptop batteries have (which connects to each cell but has only a single circuit board). Your cells may be specialized or different chemistry from “standard” 18650 liIon cells, so I really can’t give you much advice.

      In general, when you buy “raw” cells they won’t come with a BMS unless you pay extra for it.

  41. Yes Jay, new battery cells have their own fuse/BMS. So I am not sure do we have to remove the protection circuit before using them. China is producing a lot this types of batteries but I am not sure and haven’t tested these kind of batteries.
    anyway thanks always for your valued explanations

  42. Hi again Jay,

    I did some research on the internet where it is stated that: Li-Ion and Li-Poly battery packs should always be used with a protection circuit to prevent the cell from over charging or over dis-charging. Choosing the correct circuit and applying it appropriately is vital to the longevity your batteries and your own safety.

    And this PCB is incorporated within the battery cell.
    So I am not sure to remove it or not before using these cells in different battery packs that have their own charging/discharging control circuit.

    here is the link: http://www.batteryjunction.com/pcb.html

    thanks again and have e great day,

    • I see nothing wrong with leaving the protection PCB on the end of the cell, IF, and this is a BIG IF….you can still fit the cells inside the laptop battery compartment.

      However, the protection will be redundant, as the purpose of the laptop battery circuit board is to control charging and discharging current to protect the cells. Redundant protection shouldn’t be a problem (unless the cell protection shuts things down before the laptop battery BMS board does, and tricks the laptop battery BMS into thinking the cell is completely dead when in fact it was just shut down by the protection circuit).

      The big issue I see is that laptop batteries typically really jam the 18650 cells in, and I don’t think the cells with the protection circuits will fit well.

  43. Hello Jay. I have an Asus g73jh (laptop). After 2 years the battery one day died. Opened it, all cells having 0 voltage. They were some unprotected LG 18650, so i bought Panasonic NCR18650A to replace them (these are higher capacity and protected). I did the diy and connected the battery to the laptop. It shows that is charging but 0% charge. Voltage is reporting normally through HWINFO64 (14.48v).

    I tried to charge with laptop closed, but nothing. It will not charge (though it’s showing it’s charging) and it will certainly not boot up from the battery alone. I checked the circuit board to find out if something is preventing it to work, and there is a Texas instruments IC (bq20z95):

    Reading through technical documents, i found the pins that you connect to reset it, but with no success. Maybe i just need to connect exactly these pins together without touching any other pins, but it’s too small. Also i found out that the chip can use SHA-1 authorization, which will prevent me running any function if it is activated. Also there is a reset function(software) but i don’t know if it has to do anything with the hardware function:/ I’m thinking of trying to charge cells manually individually but i have no charger, plus now the tabs are welded together.

    I’m stuck now, i don’t know what to do. These cells were not cheap either..Any help is appreciated. I can post pictures too.

    Kind Regards,
    Ken

    • Hi Ken,

      It sounds like you have done much of what you can to try and re-set the BMS chip. I’m afraid I don’t have any specific advice to offer on that front.

      How do you know it is not charging? Perhaps it is charging, but the BMS is not delivering power to the laptop? Typically when you purchase LiIon cells they come with at least a 1/2 charge from the factory. You can use a multimeter to check the voltage level of each cell (and all cells in series).

      If you have a current regulated bench power supply, you can use it to charge single cells (or the entire series of cells) if set to the appropriate voltage and a low current (e.g. 0.1 amp).
      Jay

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