The battery in a Defender is under the passenger seat. It is a large compartment which you can actually fit two batteries in. This is perfect if you want to use there vehicle for winching, camping or over landing.

The main driver for fitting a second battery in our vehicle was to run the fridge. We have a Weaco CF-18 cool box style fridge this is an excellent fridge, which is sufficent for us on holidays camping, it has an 18 litre capacity. If we where going on longer trips I think I would push to get a large capacity fridge.

I wanted to keep the control and wiring simple when I installed the second battery. In order to do this I decided against control electronics, there are loads on the market made by people such as National Luna. I decided to use the method shown below.

The two batteries are simply linked by a contactor with a large rating. I chose a 120 Amp contactor in the end. The control of the contactor is by the charge indicator in the dash. I picked this up of the back of the alternator wiring to save me running wires upto the dash board.

Attached to the auxilary battery is a small six way fuse panel this allows me to fuse any additional items I attach to the system.

Here are a few pics of the layout, before additional connections where made.

Around the vehicle I fitted surface mounted 12 volt sockets, such as below the second row seats and above the rear light cluster.

There is some more info in these threads. Here and Here.

Sorry about the crappy pictures I took them on my blackberry…