This LRO reader emailed LRO.firstname.lastname@example.org looking for advice on towing a caravan with his Discovery 2.
I now use my Disco 2 mainly for towing a caravan around the more remote parts of the British Isles,so I’d like the reassurance of a back-up battery booster that I can charge from the vehicle when mobile.
The AA tested the Land Rover’s battery and says it’s fine. Even so, I want to be sure I’m covered for an imminent month- long trip into the far north-west corner of the Scottish Highlands so I’d appreciate your assistance.
James Whittaker,Newton Aycliffe, Co Durham
A battery booster is only a box with a small-capacity gel battery in it, intended to assist the main battery
for starting: I don’t see where it fits in with your situation. What I think you need is a second battery charged from the vehicle alternator, which you can fit it in the caravan or the vehicle. If it’s in the vehicle, remember that it’ll charge every time you drive off-site and you won’t have to go to the bother of moving it from van to vehicle.
The situation is further complicated bythe long charging time of any battery on a vehicle. The maximum charging rate is about 15 amps and falling. So for a reasonably sized battery you need something like an eight-hour drive to refresh it.
Modern vehicles have a computer- controlled alternator, which isn’t compatible with fancy electronic split-charge systems. All you need is a 30A relay and some 6mm sq cable: 87 goes to the vehicle battery +ve and 31 to the aux battery +ve; 85 goes to earth and 86 to the aux wiring switched by the ignition switch. Don’t, as some people advise, connect the warning light systemof the alternator.
Personally, I would advise a battery that’s the same size as the vehicle’s so you can swap should one fail.
If you want a booster you can charge it in the same way as described above – but use some sort of plug so the connections can’t touch the chassis.
This workshop advice appeared in the December 2015 issue of LRO. Back issues are available to download on digital devices here.