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Dual Battery Wiring

The following diagram shows how two batteries would be connected together using just an isolator.  This is similar to the system I used, except my isolator is wired through a switch on the dash and powered through the fuse box instead of the coil.

This is a PARALLEL configuration - where both like terminals are connected.  In between the two POSITIVE (+) wires, you can place a simple battery ISOLATOR.  The isolator is then patched into the coil.  The job of the isolator is to monitor the drain of both batteries, and recharge whichever battery that needs it the most (so it automatically switches back and forth).  I believe in this configuration, the amperage of both batteries is always present in the system, and both batteries are always being used.  Thus, if you drained your system, you would have drained both batteries!   Even though there would be two batteries under the hood, you would not have a "back-up" battery if you needed it.  That's the added advantage of the Battery Manager System I installed; as you can switch off the dual battery mode when you don't need it and keep one battery in reserve.