Originally Posted by 1l243
Ok, dumb question. Why do I need a battery cut off switch? I have four 12 volt Deep Cycles...
You don't need a battery disconnect. It is simplest to just wire them in parallel. In general, a disconnect allows control over charging or discharging of the batteries. Some common reasons to use a disconnect on a trailer with 12-volt batteries in parallel are:
Mostly ease of disconnect during storage over long periods or whenever the trailer is not in use.
The ability to isolate banks (two banks of 2-12volt batteries each in your case). You can use one bank if desired and hold the second in reserve. This is an option some people like to have - basically turning their 400Ah bank into two-200Ah banks. They can draw one bank down to 50% SOC and then conveniently switch to the reserve bank.