Parallel batteries at different state of charge

[Gould]

I’m making great progress on my install. Batteries are now complete and hooked up in their permanent location with 50% of the solar array providing power. Batteries are CATL, 271 ah x 8 for two 12V batteries. The cells were top balanced in parallel and at the relative same state of charge via BMS status. Knowing they wouldn’t be connected to a charging source for a while I connected them into individual batteries then drew them down to about 50%. The problem is I did that for each individual battery, not the two of them in parallel.

The solar panels have been providing power for a couple of days and when I look at the state of charge via each BMS one is at 95% and the other is at %75. If I just keep them connected and charging will they eventually hit the same SOC?

 

[fire hazard]

old post i say yes as long as one of the batteries isnt damaged

 

[newbostonconst]

I would put a resistor load across the high one/ones and bring them down quicker. The BMS will likely do it but could take weeks....

Good Luck...

 

[RCinFLA]

Depends on balancing bleed current verses charge rate. Usually charge current average is greater and one cell will hits its overvoltage limit in the BMS and shut down the battery pack.

The balancing bleed will continue and BMS will re-engage when overvoltaged cell drops enough voltage. This process of BMS shutting down may repeat several times before cells get balanced enough for charge controller to fully charge array and normally cut back charging.,

If BMS balancer is just a bleed resistor of 100mA or 200 mA this could take a while.