spannersatcx, thanks. However, notice that the excerpt you've quoted doesn't mention the maximum current which is allowed to be pulled from the battery.
I guess this question is not actually as relevant as I thought it was.
I've come to the conclusion that main battery overload cannot happen unless there is a short circuit somewhere, in which case its CB will react.
Main battery is not part of load-shedding scheme which is what I'm trying to simulate (among other things).