I own three 7.5AH Ego batteries. My earliest had a manufacture date of 2014 (although I purchased it in 2017 with a mower manufactured in 2016). I now have four years of operation on this battery.

As shown in the graph, the capacity dropped off over time (down to a low of 260 watt hours in year 3, which is 63% of the original 410 watt hour capacity), but in year 4 it has actually increased a bit to 290 watt hours (70% of the original capacity).

My 2nd 7.5AH battery was purchased in July of 2018 (manufactured in May of 2018).

As you can see, its graph has gone down, and so far hasn’t popped back up.   At the three year mark it is also down to a 260 watt hour capacity (63% of it’s new capacity).

My third 7.5AH battery has a 2019 manufacture date, but it’s still in its first year of “use”, so I don’t have a fancy graph for it yet, although I have started to include it in the comparison bar graph below:

So far, all three of my 7.5 AH batteries have followed a very similar capacity vs time curve, and you can expect one of these batteries to retain an average of 90% capacity in year 1, 72-75% capacity in year 2, and 63% capacity in year 3.

[Plus, they MAY bounce back up to 70% capacity in year 4, if the other two follow the path taken by my first battery.]