I wouldn't recommend mixing old with new but if you really want to carry that many batteries, use a Perko switch and keep the battery banks separate although you won't be able to capitalize on Puerket effect. Plenty of stored 12 volt power is important when camping off the grid, but just as important is the method used to replenish battery bank. We use our genny for high current draw items for an hour or so a day anyway and our Iota IQ4 converter does a great job of quickly replacing consumed amphours. Converting to LED lighting a couple of seasons ago nearly had the effect of doubling our 12 volt reserves while off the grid and is an essential mod if most of your camping is done without shore power.
