[csvencer]

That switch is designed to run two of the same batteries separately, ie. two starting batteries that are charged and used separately (unless on both, obviously). If you have a deep cycle and a starting battery you want to get one of the off-on-combine switches and a charge relay. The off-on-combine allows you to turn on both batteries on their own circuit (electronics on the deep cycle, motor on the starting) and the relay lets you charge both when the boat is running. If for some reason your starting goes dead then you can switch to combine and start off them both, if you run your deep cycle dead with the stereo, you still have a perfectly fine starting.

Make sense? It's easier to show someone, so if I didn't explain it I am sure I can whip something up in MS paint!

-Svence