Balance charging and BMS' on eBike batteries

[ki11a]

I read this article but its a bit complex: https://batteryuniversity.com/article/bu-803a-cell-matching-and-balancing


Will an ebike battery still require a balance charge every once in a while even with a BMS? I think the BMS does not matter for balancing unless it is an active balancing system which ebike batteries will not have, so a battery with an advanced BMS should still require balance charging every once in a while. Is this correct or am I wrong?

 

[harryS]

Yes, you should do a balance charge on your battery occasionally to bring all the cells back to the same voltage. This assumes your battery has balance capability. Not all ebike batteries use them, as I have found out. In fact, I'd guess that few of the inexpensive models and probably none of your budget third party batteries do so,
.

 

[m@Robertson]

Its a good practice unless you have a pack that comes on a manufactured bike that specifically tells you not to do it. On a daily-use bike, here's what I do:

1. Charge to 80% normally - typically thats 2x per day for me.
2. Once per month, charge to 100% and let it sit on the charger for a couple of hours @ 100%. This is your balance charge.

On that balance charge, I typically use a Grin Satiator as its got a reliable voltage setting. You can typically *see* the pack balancing as the display will read 'charge complete' for a few seconds, then it will pop out of that mode to charge for 0.1a or 0.2a for a few seconds, then a brief stint back to 'complete' and the cycle will repeat itself. When the charger sticks solidly on 'complete' the BMS has topped up everything and you are balanced. So while I say 'leave it at 100% for a couple hours' the precise method would be to monitor it and pull the plug when the display tells you its not topping up anymore.

For your typical cheapie Chinese charger you'll have to just let it sit awhile as they have no display.

If you have your packs made by a quality pack maker, they will spend some time testing the cells and sorting them by hand so they can use cells that are already a close if not exact match. At that point, its a lot more likely that you can get away with balancing the pack once when you get it and leave it for a much longer time thereafter (as in forever, theoretically). My packs are made like that but I still do a monthly 100% balance.

 

[ki11a]

I am getting told by a manufacture that their Retention eBike battery BMS' make it so balance charging is unnecessary....I am skeptical.