[Riwright]

+1 on Davlins comments, a good summary of the endless Thetford threads.

There are two basic types of batteries. Starting batteries or deep cycle batteries.

Starting batteries are made for cars. They put out a large rush of current for starting. They do not do well when they are heavily discharged.

Deep cycle batteries are made to put out smaller amounts of current over a long period of time. They do well when heavily discharged.

6 volt batteries are made for golf carts and arre true deep cycle batteries. They do very well with the type of use that you see in a typical RV. If you put two of them together you get the 12 volts you need to run the RV systems.

Another type of battery is a "Marine" battery that is a compromise between the starting and deep cycle batteries. Most single battery setups in RV's use a Marine battery.