Simple Dual Battery

well you already have the idea for simple just run some big wire i run 2x6mm from you alternator to a hand opperated cut of solonoid to your second batt simple as that just remember to cut of when you stopped

alternatively use an electrical solenoid ($80-100) to isolate the battery when you turn the ignition off. My preference would be to wire the deep cycle where the starting battery is, and then connect the starter battery through the solenoid. With the fridge wired in to the deep cycle (using 6mm cable for preference) once you turn the ignition off the starter battery is completely isolated from everything, ensuring you can start up next morning, and the deep cycle is running all the vehicle electrics - including courtesy lights/headlights which sometimes come in handy in camp.
Cheers,
Alex.

ok a hand operated solonoid has power going to it from your bat/alt available from repo ect with a knob on it wich you turn to switch the current off so what happens is when your driving you have the power running through the solenoid and when you stop for the night you turn the switch of so if the second battery goes flat it cant draw power from the starter batery.or you could bye a power solonoid i got mine from repco for about $40 when you wire it up there is two main power points where you send power from the alt/main battery in on one side and out the other side you wire it to your seond battery and it has another power point that you have to wire to your ignition so when the ignition is on it opens the solonoid alowing power to go through to the second battery but once the ignition is switched of it shuts the solonoid automaticaly so you wont drain your starter battery hope i was not to confusing. looking foward to easter at jamieson