danyro wrote: ↑
Mon Nov 25, 2019 12:02 pm
thanks for explanations and reference.
so the best method without too much hassle, would be the 2nd option.
But maybe someone with electricity skills/know how can say if charging port of external battery would be connected to the original internal battery port charging and in the same time, it will charge both batteries via their designated charging port, at the same voltage...
dont know if this would be a feasible scenario ..
That setup you describe sounds like the worst scenario mentioned by Rollerplaush:
"Charging by both chargers - charging time 4-6 hours (negligent)
Here the BMS can not work as intended! Depending on the combination of the batteries , the following occurs in addition to an uncertain final voltage :
Y-Method : The BMS of the auxiliary battery can not switch off due to the Xiaomi charger, which contributes via the discharge port! "
And it doesnt accomplish anything that charging via the second batteries charging port wouldnt, it just adds extra danger. Both batteries will still charge to 42V, because they are connected in parallel and will equalize no matter what. If you dont want them to charge to 42V to prolong charge cycles, you can limit the charger to 41.5V or 41.0V, but that might be problematic: if you use the cheep aliexpress batteries, they will require to charge to close to 42V for cell balancing.
I woulnt worry much about reduced charge cycles, because you will have two batteries and each battery will be used less, equalizing the loss. Might be even better because the batteries wont heat up as much as less current is drawn from each one, prolonging their charge cycles/ life.
The part about regen braking not working when battery is at 42V is omething you want to test - does it really not work and how much you have to drain the battery for it to start working again. Shouldnt be a big deal once you know it.