this is how mines wired and i've had no problems at all;
front battery-----front fuse (within 12" of batt - i used 150amp but you'd get away with less)--------------------4awg power cable-------------spitcharge relay---------------rear fuse (again within 12"-----rear battery.
obviously you've to earth the rear battery.
split charge relays are made by autoleads and should cost around 25-30quid (think even halfords do them)
the relay has 4 connections on it, two large screw down connections which the power cable from the front battery and rear battery connect to, and two smaller blade type connections -ones your earth and the other is the remote as such to 'connect' the two batteries together.
i wired the remote connection to the live from my electric windows. this way when i put the key in the headunit works and the system (apart from the hu) is running from just the rear battery - technically you could cane it until it ran out of juice and still be able to start up and dirve away. ?then when i turn the key one click forward so the warning lights come on the windows also become active thus the charge relay is activated and the front and rear batteries are linked. playing without the engine running and the key at one click would eventually drain both batteries though. and obviously when you turn the key to start the engine both batteries are linked and subsiquently both will charge. ?as a rule of thumb with this system if the windows work the batteries are linked - if not their not ?
hope that helps - theres a pic of my battery and relay and rear fuse in the post on making pods - you can see the realy dangling off the rear light cluster
hope this helps
