Dual battery installation in a 1995 Defender - minimal modifications

[SmalltimeExplorers]

Hi,
when I was considering putting a second "house" battery on split-charge in my Defender (1995) there were very few specifics on what parts people used. This post is intended to rectify that.

Why a second battery on split-charge?
To reduce the number of times we needed to visit shops while camping or exploring by allowing the electric cool box to run for as long as possible.

What?
The starting battery remains an 096 lead-acid type.
The house battery is a Varta LFD75 with the part number being 930 075 065 B91 2 this is a 75Ah lead-acid type.
The split charge control module is a 12V 140amp Durite 0-727-33 voltage sensitive/intelligent Split Charge Relay
Circuit protection is by means of ATO fuses in a 4-way fuse box, a 20 Amp fuse protects the battery live connections to the starting and house batteries with a 15 Amp fuse for the single cigar type outlet.
The wiring is 4.0mm CSA thinwall automotive wire with split conduit protection.
I made a custom battery clamp which re-uses the OEM clamp bolts and adds a third inboard to keep the batteries secure, the clamp has flanges on each end to stop the batteries from migrating laterally.

Where?
It all fits in the LH seat box locker with the split charge relay mounted next to the "immobiliser" and fuses beneath the outboard lip. The only drawback is the loss of stowage space but I'll happily trade this for the ability to avoid shops.

The installation is on test at the moment with a camping trip planned for next week.

I'll post photographs if there is any interest.

 

[hillstrubl]

interest for photos #thisguy

 

[DiscoDavis]

It has been done with a lot of defenders. The battery types vary so its up to you. The most help you can be to future people trying to do a dual battery would be to post good photos and explain the wiring or diagram it.

I think I (like a lot of people) did mine with a big solenoid that runs off either a switch or a manual cutoff so that you have on live battery to run house or camp off of and then one that sits solely for starting. I fused the batteries with those big ANL fuses and put everything I added (non factory electrics) in a blue sea 12 slot fuse box

I wished at the time more people diagrammmed it out but its easy to figure out too.

 

[SmalltimeExplorers]

I'll put up a wiring diagram with part numbers but the key thing for me was to make the installation "OEM" quality.
I've seen too many photos where the installation looks a major fire risk.
Best refinement I've made to it is to add a low-voltage cutoff to the outlets supplied by the "house" battery - many powered camping devices don't have a low-voltage cutoff and will happily drag the house battery down to 7 or so Volts before their internal electronics no longer function.

 

[SmalltimeExplorers]

Here are some general views of the installation as I added the low-voltage cut-out to protect the supply from the house battery to the power outlet. The cooler I am using is nominally 50 Watts and the fuses to/from the automatic split charge module are 30 Amp. These I think need to be rated a bit higher because they fail due to long-term thermal effects when travelling from home to camp. I need to take some measurements and see what is happening so I can figure out the best solution. Wiring diagram to follow..