Stromer (and other) Battery Saver - Increase the life of your battery 3+ folds

Batteries for ebikes cost a fortune, yet manufacturers sell batteries with chargers that charge batteries always to the max (unless you unplug the charger before the end of the charge).

by charging your battery to 100% each time you can expect c. 300-500 Cycles. By charging to 80% instead, you lose some range but can expect c. 850-1,200 cycles from the same battery, or more, i.e. a 3 fold increase (source: https://batteryuniversity.com/article....

The device depicted in this video is nothing more than a voltmeter that switches the supply of the charger off whenever it reaches a pre-definied level of charge. This requires no modification to the battery itself, just a minor modification to the battery charger (basically welding the two wires to the '+' and '-' of the battery charger so it can measure the voltage that goes to the battery.

Since battery cells can get off balance and because BMS (Battery Management Systems) typically rebalance the cells when almost fully charged or fully charged, it is necessary to run a 100% cycle from time to time to get the "balancing cycle" starting. Quality battery cells used in batteries like the Bosch, Shimano, Stromer bikes do not get imbalanced that easily, so my guess is that running a full cycle every month or couple of month should be sufficient to get your battery cells rebalanced.

As a disclosure, this is just an explanation of what I did on my own charging system and it is not an incentive for you to do it. Should you do a similar project, you need to understand the risk and would do such project under your full responsibility. If you do not have basic understanding of electronic and electricity, I advise you NOT to do this project and NOT to modify anything on your ebike charging system. Here specifically, we are dealing with 220V so this is dangerous if you do not know what you are doing.

Also, should you do such a project, expect the warranty on the charger to be void since this requires a modification of the charger.

Additional disclaimer: do not expect it to work on "Constant Voltage" chargers (often found on cheaper ebikes like Decathlon bikes for instance) as they always send the same voltage to the battery irrespective of the state of charge of the battery; hence the "Stromer Battery Saver" would not be able to measure the state of charge and would be totally useless.