When we had the caravan in the UK and went to a sheep farm without hookups for 2 weeks in the summer, I decided to fit a second battery to my Discovery 200TDi. Installed it where the jack normally goes, moved said jack to a location next to the brake servo, and wired batteries (identical layouts for interchangeability) with the live connections permanently hard-wired with the normal thick red battery cable. I fitted one of those DISCARNECT (I think they're called units) to the negative terminal of the second battery and earthed the other end to the body nearby.
Unscrew & remove the connector screw and the second battery is isolated from the normal battery. Replace the screw and both are connected in parallel, so you can then charge both together. I also fitted an "S" socket under the front bumper so that I can use a 3-pin flat chocolate block plug/socket (from Maplins, on a strip) such that if I connect it one way it charges one battery and when I reverse it it charges the other (assuming the Discarnect screw is removed) without even raising the bonnet. Still use it here to this day. Simple and effective, no electrickery, relays or any of that carp.
- Richard
