I don't think that is what this person is talking about. Yes having an extra lower voltage battery is totally normal and every EV either has a led acid or an ad

I don't think that is what this person is talking about. Yes having an extra lower voltage battery is totally normal and every EV either has a led acid or an additional smaller LiIon battery. Having multiple chemistries in one battery pack is of course possible, but I don't any car who is actually doing that.