Addin another bat

How do I wire in another battery into my system..?

depends on where you want to put it. If you want to put it in the back near the amps, you basically wire it in just like another amp. The + terminal will go to + side of the main battery OR to the + distribution block, the - side goes to metal chassis or back to the main battery. Your choices on how you wire it depend on the power you are running.