Putting two batteries in parallell is a *bad* idee. Supppose one cell of one battery shorts internally. This happens frequently with automotive batteries. The one battery then becomes a 10 Volt battery and the other one will send an extremely high current to that battery which can actually cause that battery to explode.
In order to prevent this you would have to put a large diode in series with each battery to prevent either battery from discharging into the other. Those diodes are big, get hot and need heatsinks. Talk to the RV people. And then there is the problem of charging the batteries because the alternator cannot put charging current back thru the diodes. Series connecting two 6 Volt batteries is the only way if you want to use two batteries. If the one is extremely far from the other, you can always use a slightly heavier cable for that one. Just my and Ohms's opinion! yson, Arizona n...@cbiwireless.com
