My battery book (by Barre) says with batteries in parallel, the battery with a lower internal resistance supplies a greater amount of current to a load than the battery with the higher internal resistance.
That looks like what Mex just said, that you need to know if the one battery is at 50% while the other is not that far down. I suppose that is what a BMS does with Li banks. No BMS with SiO2.
The batteries will never be exactly equal in construction or degree of sulphation on the plates, to have exactly equal internal R but same type and age sure helps with that.
So, looking up on internal resistance, problem! There is DC and AC methods for measuring it, and AC method is better for loads like inductive motors vs heaters and it all gets complicated. Except AC method is impedance Z, not ir R. Whatever!
I don't know if the draw from a MW on an inverter (seen as inductive by the inverter) is also seen as inductive by the battery the inverter is on. Anyway, charging ahead regardless:
Car battery - 0.02 Ohms (whatever that is in mOhms--brain quit!)
100AH 27 size AGM- 5 mOhms
100AH 27 size SiO2-=< 6.8 mOhms (at 77F)
Charging specs: AGM- 14.5-14.9 cycle use, 13.6-13.8 float use
SiO2- 14.4-14.7, 13.5-13.8
Wiring is part of the internal resistance actually seen between load and battery and between batteries so that can double the battery's own.
