09/06/10

When installing more than one battery for use with the 12 volt RV system, it is recommended to purchase the batteries at the same time. The batteries should be matched with regard to capacity, brand, and age. This will give you the best possible life from your RV battery bank.
RV Battery Voltages

RV Batteries are constructed to supply 12 volts or 6 volts (for the purpose of this article).
In most cases two six volt batteries will have about 20% more capacity than two similar sized 12 volt batteries. This is due to the larger plates that are built into a six volt battery.
RV Battery Circuits

Two 12 volt batteries are connected in a parallel configuration with the two positive terminals connected together and to the positive trailer lead. The negative terminals are connected together with the trailer negative lead.

Two six volt batteries need to be connected in a series circuit in order to get the 12 volt needed to run the coach system. In this case the trailer positive lead is connected to the positive terminal of the first battery. The negative terminal of that battery is connected to the positive terminal of the second battery. Finally, the negative terminal of the second battery is connected to the trailer negative lead. The size of the jumper wire should match or exceed the size of the trailer leads.
RV Battery Polarity

It should be noted that the positive lead from the trailer is normally the black colored wire(s) while the negative lead is the white colored wire(s). This is sometimes confusing, as most automotive applications use red as the positive and black as the negative. Polarity is very important to the electronics and the various motors in the RV and must not be reversed.

Note: battery terminals (or posts) are marked with a plus sign for the positive terminal and a minus sign for the negative terminal.

To make it even more confusing, makers of after market items, such as solar panels will have the red wire as positive and black as the negative.

Before disconnecting your RV battery for any reason, it is suggested that you tape the wires together near the terminal that they are attached to and then mark them with respect to what terminal they go to. This will avoid confusion and reversed leads when re-connecting the terminals.