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I want to put another battery in my 01 Forester for my fridge. I would like to know if anyone has all ready done it. My mate at work; in his Patrol has done it like this; all he did was just ran a battery cable from his positive '+' on the car battery to the '+' on the backup and a cable from the backup '-' to the block. He has had his car wired like this for 12mths now and has had no problems. What do you guys think?

That will make both batteries last longer (and charge slower), but won't stop either from being run flat if you leave the fridge connected with the car off for days.

Best to use an isolator of some description so that the fridge etc will only run down your second battery, and the main starting battery will still be able to start the car in the morning. The isolator can be a big switch, a big relay switched by the ignition, or a whizz-bang voltage sensing "smart" relay.

there's a bit more discussion here: showthread.php?t=13791&highlight=dual+batteries+series

Dane.

Note that if the batteries are non matching (like if you get a large deap cycle unit for an auxillary) you need a really smart charging system. If they are just wired up in parallel apparently they will just not charge correctly.
If they are identical batteries you can do it really cheaply by using a simple isolator switch with the positions 1, 2 or BOTH selectable. These switches only cost about $50.

Get your hands on Australian 4wd Action, issue number 141 there is a big write up on dual batteries/isolators

I have been running a voltage senitive relay(VSR) for my dual batteries for over three years now, and touch wood it has worked perfectly, I use it to charge two deep cycle marine batteries, one is my start battery and the other is for the fridge etc. I was told to get this type of battery as they are designed to charge faster than a normal deep cycle type battery and are therefor more suited to the sort of use and abuse they get in a car.

Cheers
Grant

I personally have an optima battery in my wagon and granted it isnt parked for more than three days but with a Waeco CD30 and the wireless going the whole time it seems to work perfectly. Although if you do a dual battery setup you dont have to stress at all although I would avoid a deep cycle battery as a starting battery as their not designed for a high instant load...

I would avoid a deep cycle battery as a starting battery as their not designed for a high instant load...

Another reason to use a deep cycle marine battery.