How ToLand Rover Defender

How to install a split charge kit into a Land Rover Defender

The twin battery set up with split charge kitOn my road trip next year, I am going to be wanting to power some accessories (laptop, interior lighting etc) in the evenings/overnight.

If I connect them to the main battery when the engine isn't running, then it will be drained overnight and I won't be able to start the Landy the next morning.

So the answer is a second battery and split charge kit. This is how I installed it.

So what is a split charge kit?

A split charge kit consists of a load of wires and relay! The relay joins both batteries together when the ignition is on and the engine running. This charges both batteries at the same time.

Now, when the engine is off, the relay disengages and separates the two batteries. This means you can run accessories like a fridge, tv or lights from the leisure battery without worrying about discharging the main vehicle battery. This means you can start your Landy again.

Fitting the second battery

As you are probably well aware, there isn't much room in a Land Rover Defender battery box. You can buy a double battery tray, or you can make up your own.

Whichever way you decide to do it, make sure that the battery terminals are well away from the removable metal battery box cover. If in any doubt, make sure all the terminals are insulated - you don't want to start a fire when the terminals short out on the metal cover!

Also make sure that both batteries are clamped down to stop them moving around.

Wiring the split charge kit

The Hella split charge wiring diagram

A battery costs are from around £80 upwards, and a split charge kit is around £30, or just a few quid for the relay if you want to make up the wires yourself.

Luckily my friend has given me the split charge kit, and I had a usable 2nd battery laying around in the garage.

To make things a little easier, I have taken a photo of the wiring diagram supplied with my kit (photo on the right), so have a look for yourself, as its pretty straight forward.

Note: Wiring the split charge kit is fairly easy, but if you are not used to dealing with wiring diagrams, or you are unsure of your electrical abilities, then take your Land Rover to an auto electrician - it won't cost much for the installation.

My kit contained a double relay, which is connected together, but a single relay will do fine. The wiring consists of the following 4 wires:

  • Wire from the positive terminal on battery 1 to the split charge relay (terminal 30). This wire contains a 25amp fuse.
  • Wire from split charge relay (terminal 87) to the positive terminal on battery 2
  • Wire from split charge relay (terminal 85) to earth
  • Wire from alternator (or an ignition switch controlled supply) to relay (terminal 86). This is the feed which activates the relay to allow both batteries to charge when the engine is on.

The twin battery set up with split charge kitOn the right is the completed set up in my battery box, with notes explaining what each wire is for. The earth wire from the relay is earthed on the screw holding the relay to the metal battery box.

There are some other wires in the set up, but I have only added notes to the wires discussed in this post.

You will be able to tell when its all wired up correctly as when you switch on the ignition, you will feel/hear the relay "click" as it joins the two batteries together.

I hope this helps you understand split charging a bit better. If you need any advice be sure to drop me an email

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