I tried to use the lithium-set 120V 10 amp battery charger that came with the batteries to charge a single (disconnected/isolated) battery. But it is too slow for using the genset. After 6 hours of run time, the voltage increased only from 13.01 volts to 13.16 volts. Or, does that prove it is the battery's BMS limiting the charging?
10 amps at 6 hours and goes from 13.01 to 13.16v sounds like it is charging to me.
It's slow, but it is certainly charging. Used a calculator, and very slightly over 3.2 to very slightly under 3.3, that is a pretty significant charge for LiFePO4. It sounds like it is accepting the 10 amp charge.
So, if I disconnect the lithium batteries and connect the lead-acid 12-volt battery, I also need to reset the Tracer charge controller to SLA, to be safe? Correct?
Yes, I think so, but I don't know much about SLA.
Edit to add, don't try to parallel the batteries until you have charged all three pretty close.