So what would happen if battery1 hits 3.65V 2 minutes before battery2? Do I have to control the BMS pair while charging?
The inverter/charger does whatever you have it set to. If one BMS series resistance is higher that causes less current to be pushed to that leg then it will not be at the same charge level in the same amount of time. But that is not a major problem.
Your inverter/charger should hold at 3.65v x 16 cells Bulk voltage setting until charger current drops to your set level or for the time limit you set as maximum bulk time. As the charge current is tapering off the voltage drop different caused by BMS series MOSFET switch will diminish, any charge imbalance will be eliminated. Having a continous active balancer is better as it provides more transfer current and runs thoughout the charge cycle, not just above 3.4v on a cell.
If you do a partial high current with early termination of charging, then maybe there will be charge difference between banks. Even if you have only one series string the same issue exists on the individual cells in the single string.
Just make sure you do a full charge with current taper-off once in a while to bring all cells to their balanced charge state. Remember most BMS's with resistor dump leakage charge balancing only kick in when a cell gets above 3.4v, so if you never take them above 3.4v per cell they never get balancing.
If you only have solar to charge and have trouble making full charge very often then I suggest you put active balancers on each string. This applies if your are running just one series string or multiple parallel series strings. Active balancers can be strapped on in parallel with existing BMS.
BMS series MOSFET heating causes their Rds_ON resistance to increase. This is somewhat self compensating as the one delivering more current will get warmer causing its resistance to increase compared to other parallel string's BMS MOSFET switch, causing the current distribution at least partially balance out between the two series banks.
If you never take charge to full bulk completion the cell balance will diverge over time (without an active balancer). Again, this will also be the case if you only have one series string.
Again, the major thing to avoid is only one BMS tripping open throwing full weight of discharge or charging to remaining active string.
BMS's do not control charging. That is up to charger. The BMS will prevent overchargng by pulling the plug on battery connection.
BMS's should be viewed as a safety fuse. It should never shut down if you are doing things correctly. Folks that are using BMS's to tell them they have completely depleted their battery are just shortening the life of their batteries and stressing their system.
