Nissan Leaf 12 volt accessory battery replacement

My wife came home one night and told me that when she had started up her Leaf for the drive home it “acted wonky” with lots of warning lights on the dash, and the brake pedal went to the floor without actually keeping the leaf from inching out of the parking space she was in.  This sounded like the 12 volt accessory battery was no longer holding a charge and was in a low voltage state (which the electronics in the car really don’t like!). This happens when the battery ages, and Nissan Leaf’s are notorious for going through 12 volt accessory batteries quickly.  (Even though the batteries don’t need to provide a lot of cold cranking amps to turn over an engine, the car electronics draw a lot of power, and the main power distribution unit will re-charge the battery at a high amp rate when the car is on. They are also a relatively small sub-compact size (Group Size 51R).  The car is 4 years old, so I figured it was about time for the OEM battery to be replaced.

When I went to examine the battery under the hood, I realized that it needed to be replaced sooner rather than later. It’s never a good sign when the special blue power crystals escape from the positive terminal lug, or battery acid eats the paint off of your battery hold down bar…

So, after spraying foaming battery acid neutralizer all over the place, I re-painted the battery hold down strap and bought a Duralast Platinum 51R AGM (Absorbent Glass Matt) battery at AutoZone that comes with a 3 year replacement warranty.  (It was  cheaper than the yellow top Optima AGM battery that is widely recommended for the Leaf, and the warranty period was the same.)

People online have said that AGM’s work better with the high current charge rate provided by the leaf’s power distribution center, and I figure that being sealed they would be less likely to vent acid over other parts of the car. I could have gone with the $70 battery that came with a 3 month warranty, but I figured that the Leaf is hard enough on it’s accessory battery that I’d better pay for the good one.

So far the maintenance needs of the Leaf have been relatively small, and this is the first major item that needed to be replaced. (New tires are coming up soon.) Other than this  battery replacement, I’ve bought new wiper blades, replaced the cabin air filter, refilled the wiper fluid and rotated the tires.

How far can it go?

Summary: I drove my truck 46 miles on one charge (and had some juice left over).
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When you have an electric vehicle, everybody wants to know how far it can go.
I typically tell them “19,800 miles so far.”

But then you have to answer their real question, which is “What’s your range on a single charge?”. If you have a commercial EV like the Leaf or a Tesla, you can just refer to the EPA range figure for a nice apples to apples comparison. But when you have a conversion EV, the number is unique to your particular vehicle, motor, controller, battery pack and testing methodology. (And changes as the pack ages…)

I used to know the answer to that question for my truck with a (new) lead acid battery pack (“25-30 miles without killing the pack”), but I haven’t fully characterized the trucks’ power usage and range with the new (lighter weight, more powerful) pack made up of Nissan Leaf cell modules. My truck is heavier and has more air resistance than a stock Nissan leaf,  the motor/controller is slightly less efficient, and the (big fat!) tires have quite a bit more rolling resistance. I figured “half the range of a Leaf” would be a good ballpark estimate.

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Nissan Leaf Modules powering my S-10 Pickup conversion

I have successfully driven my S-10 Electric Pickup conversion powered by 48 modules from a salvaged Nissan Leaf battery pack. I have them wired in series, 16 sets of 3 parallel modules, providing 128 volts with 180Ah capacity (23 kWh).

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It took me a full three days of work to make the swap and get the truck to a barely drivable condition. I have the cells hooked up with a warning buzzer on the BMS low voltage loop signal, but I do not yet have the charger fully connected. I anticipate another 8 hours of work to get the charger and pakTrakr system fully set up.

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16 volt Nissan Leaf Battery Management System (BMS) information

In a previous post I have shown how to physically mount six Nissan Leaf battery modules in two series groups of 3 parallel modules to build a 180 Ah by 16 volt Lithium (LiNMC) battery.

The batteries are covered by these very cool laser cut acrylic protective covers (which obscure the BMS wiring).
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Anthony Felix asked for more information about the BMS units I’m using on my batteries, so here it is! (Jump down to the last picture if you just want to see where the BMS units are attached….all of the text between here and there is an explanation of WHY they are attached there…)
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Economies of harvesting Nissan Leaf battery modules

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I purchased a 2013 salvage (wrecked) Nissan Leaf from the CoPart auto auction house for $4081 (including delivery and fees). I consider this to be a very good price for a wrecked Leaf, but if you stalk a lot of auctions and bid on Leafs that have the most damage you can probably get a similar deal with enough patience.

Then I spent 439$ on the following tools that I needed to move the car around and extract the battery (the largest amount was for jacks and wheel dollies…)

Car Cover (Keep the neighbors happy) 37.1
Wheel dollies & Jacks 243
Bluetooth OBD II scanner 9.98
Leaf Spy Pro android app (to check battery) 14.99
500V gloves  (Safety first!) 21
2 Jackstands (already had 2) 25
Air Impact Wrench & Sockets 46.5
18mm wrench 12.4
13mm deep socket 8.99
21 mm combination wrench 20.69

This puts my total costs at 4520.75 ($94.18 per module) for a 24 kWh battery pack, which is less expensive than if I bought large format prismatic cells.

Of course, with a lot of time and effort, you can sell all of the other parts from the car. Over the course of six months I made back $3180.46 (including the sale of the smallest of the three jacks I had purchased and 0.46 in change I found in the car.) I’m posting this after selling the main body of the car, leaving me with just a few small items listed on ebay. I may earn a few hundred extra dollars over the course of the next several months, but the overall cost recovery is finished.
final_sale

My current total out of pocket expenses (not including lots of labor!) is 1340.29 (or $27.92 per module) which is quite a significant savings over other options for purchasing large format Lithium Ion batteries.

I’ve seen Nissan Leaf modules selling on Ebay for around $130 each with shipping (in larger quantities), so my ~ $30 per module cost is around 21% of the cost of purchasing them on the used market.

To put this cost savings in perspective, purchasing 20 lead acid golf cart batteries to replace my current pack would probably cost me around $2000-$2200, so the Lithium Ion Nissan leaf battery pack was actually less expensive than a replacement lead acid pack!

However, the process of parting out the wrecked car takes a lot of time and effort. If you are just after the battery and can find one for sale at a salvage/junk yard for less than $2500 it would probably be easier to buy the battery alone without the rest of the car. The one advantage of purchasing the whole car is that you can (sometimes) find out how many miles are on the battery pack. In my case, I was able to use an OBDII scanner with the Leaf Spy Pro application to find out that my battery pack health was still at 98% before I removed it from the car.

If I were to buy a whole car again, I would try much harder to sell the entire car (minus battery) in the $2000-2500 range before parting it out and trade some money for my time.

The Nissan Leaf pack weighs about 650 lbs less than the lead acid batteries currently in my truck. They are capable of providing more amps with less voltage sag due to lower internal resistance, and more of the pack capacity is usable as they don’t suffer from the Peukert effect as much as lead acid batteries.

The overall performance of the truck should be much improved. Also the battery life should be much longer than 2 years. (Cycle life for lithium ion batteries is measured in thousands of charge cycles, instead of hundreds of charge cycles for lead acid batteries.)

However, because I am changing battery chemistries, I am also upgrading my trucks’ charging system (and home EVSE) and those costs are actually more than the battery pack, so the total upgrade cost will be more than just getting another lead acid battery pack. (I will talk more about charger upgrade costs in a later post).

How to build custom length high current cables

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When wiring up an electric vehicle traction pack battery, an off-grid battery backup bank, or other high current power systems, you sometimes need a cable capable of handling high-current with a custom length. If you have a few tools, it is easy to make your own by crimping terminals onto welding cable. This video shows a time-lapse overview of making such a cable:

Here is a set of links to the tools and materials I used:
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Battery carrier compatibility, location specific modifications

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This is a Battery Carrier tool designed for picking up and carrying around lead acid batteries (golf cart or starter batteries). I own one because it’s very useful when removing 20 golf cart batteries from my S-10 electric pickup truck and replacing them with 20 new batteries. While manhandling my Nissan Leaf batteries around my garage, I though “Boy, it sure would be nice to be able to use my battery carrier on these guys.” A few minutes spent rigging up a jig for my trim router and vacuuming up a lot of saw dust later, each of my batteries has a small slot cut in both sides…

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I had thought that I would have to sell my battery carrier and battery filler now that I am upgrading to Lithium Ion…I guess only the battery filler will be obsoleted.

I also modified a few of the batteries to better fit in my existing battery bays. Specifically, I decided that batteries 1&2 and 7&8 would be mounted “back to back” and I didn’t need each of them to have a full 1″ of space at the bottom, so I cut a 1/2″ off the bottom of each, giving me an extra inch of room, and leaving them a shared 1″ air vent.
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On battery 3, which will be mounted “sideways” with respect to batteries 4,5 & 6, I used a spade bit to sink the washer in a little, and cut off the ends of the threaded rod to make sure they wouldn’t interfere with cables.

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How to build a 16 volt battery module from six Nissan Leaf cells

I am building 16 volt batteries using six Nissan Leaf LiIon cell modules. (A Nissan Leaf battery has 48 modules, supplying the construction of 8 of my “batteries”.) My Battery is arranged in a 3P2S (two sets of 3 parallel modules in series), giving a 180 Ah capacity and nominally 16 volts (each module from a Nissan Leaf has 2S2P cells inside, so the module goes up to 8.4 volts maximum at 60AH).

This video (playing at 4x-16x speed) shows all of the work that goes into building a battery. Directions with more information are below.

To build a battery, here are the parts you need:

  • Two end plates, made from steel or plywood.
  • Six nissan Leaf modules, sandwiched between the end plates.
  • Four pieces of threaded rod, 10.5 inches in length, with the following hardware for each rod:
    • Two nuts
    • Two lock washers
    • Two fender washers
  • One 7.5″ x 1″ x 0.25″ copper bus bar (to make the series)
  • Two 3.5″ x 1″ copper bus bars (to join the sense terminals) I used 0.25″ thick so that I could source it from the same copper as the series busbar above, but this is overkill, you could use 0.125 or even smaller.
  • Two 3.5″ x 2.5″ x 0.25″ copper bus bars (to be the + and – terminals of the main battery).
  • 12 M6 bolts (can re-use the ones that came with the leaf modules)
  • 12 M6 Locking washers (I used Belleville Spring lock washers)
  • six M4x16 machine screws for the sense terminal bus bars
  • six M4 locking washers (I used Belleville spring lock washers)
  • three M4x8 machine screws for the BMS terminals + 5 more lock washers
  • Two 5/16th bolts (1″ or 0.75″) for the + and – terminals. (could substitute 1/4″ or metric bolts, I used 5/16th because that is what golf cart batteries use.)
  • (very optional) one more 5/16th bolt for the series bus bar if you want to attach a 5/16 ring terminal from an existing battery monitoring system to each “8 volt” half of your battery.
  • 12×12″ acrylic sheet to laser cut battery cover from.

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Laser cut acrylic terminal covers

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I laser cut some covers that place an acrylic wall between each of the busbars of my battery, as well as covering the top. They are designed to keep a falling screwdriver, wrench, or bolt from bridging the bussbars and causing “excitement”. I have a lot of air holes to try and allow a normal amount of air flow, as well as exposing the bolts and screws for occasional tightness checks.

busbar_layout

You can download the textual openscad design file here:
battery_shield.scad

Or, you can just download the PDF files if you want to laser cut them exactly as they are:
battery_shield
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A “how to assemble” video is here:

Youtube Video link

Acrylic could be a bit brittle for this application, and using 3mm craft plywood could provide a bit more impact resistance. However, the covers are inside the “sidewalls”, plus the batteries will be mounted sideways and the current “top” will be mostly protected by insulating foam in my battery boxes,so I chose to go with the less smoky option. (Plus, I think the semi-transparent nature of the acrylic just looks cooler.)

Leaf battery module differences – 36 “normal” and 12 “special”

The 2013 Nissan Leaf battery pack that I disassembled had 48 battery modules in it. Previously, I had separated the modules that were in the front half of the pack, packed in stacks of 2 or 4 “flat packed”. However, I had only removed the 24 modules are located in the back of the pack (under the passenger seat) as a unit, and had not unpacked them yet. When I unpacked them, I discovered that 12 of the modules (every other one) had some differences from what I consider to be the “normal” modules (the other 36).

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In the picture above, a “normal” module is at the top, while one of the 12 “special” modules that supports the mounting brackets is on the bottom, with the removed mounting bracket. Note how the tin plate sticks out a little bit more on the “normal” module, taking up the same amount of space as the steel mounting bracket on the “special” module.

The “special” modules have small metal plates that mount to the top and bottom of the modules. These metal plates then bolt into support brackets, which allows this set of 24 modules to be supported “sideways”. I started to worry that these extra pieces of metal would change the spacing of the modules (from my previously measured 1.3333 inches per module), but as it turns out they don’t. The modules themselves are shaped slightly differently (just a bit narrower at the top and bottom) to allow for the extra width of the steel mounting brackets. The main body of the modules should still be compressed to 1.333 inches in size.

Looking inside, the pouch cells extend up past the main body just slightly, so I decided to leave the steel plates on as shims, but cut off the bolts as they would get in the way of my busbars. The bottom of the pouch cells don’t extend appreciably past the main body on the bottom, so I’ll be leaving the bottom steel plates off.

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The metal plates have circular tube like supports that reach inside the holes on the modules, supporting them, and are also spot welded to the thin “tin” outsides of the modules. They can be pried off with a flat bladed screwdriver, popping the spot welds out and leaving small holes in the tin plates.

I just used a cut off blade on an angle grinder to cut off the parts of the brackets that I don’t want hanging out on the top of my battery.
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