mystery wires! Duel battery?

I'm trying to get to grips with the electrical system on my 1996 defender.
Inside my battery box i have a wire with battery terminal clamp on it the goes into the bit bolted to the side and there's also a wire coming out of that, that goes to a couple of relays, one being a land rover voltage sensitive one then theres a couple more lose little wires floating about.
I'm guessing its factory installed looking at it but i can't seem to find anything out about it.
I plan on adding a 2nd battery to run winches from so this would be handy if the wiring is already there but i don't want to chuck a battery in and start hooking it up without knowing?

Your winch should be connected to your starter battery.
Split charge switch see here......
Split Charge - From DA310169 To MA962814 - Find Land Rover parts at LR Workshop

A winch will flatten a battery quite quickly, within a few minutes of continual use .... you should have the winch connected to the main battery and run the engine when winching under load.
A second battery is used to provide 'engine off' power for inverters, a camper fridge, radio or lights etc the yellow LR voltage sensitive switch and the relay is there to charge the other battery when the engine is running as long as the main battery is charged (ie it prioritises the main battery so the car will always start).

Winches are connected directly to the main battery via an isolator, they require two very thick, high current cables (rated at around 500A).

That's great cheers.
I will have a dig around in there later and take stock of all the loose wires i have in and see if i can make sense of it.
Am i right in thinking that clamp i have connects to positive on the new battery and then i join the earths of the batteries together? then like you said, if its working correctly once the main battery if fully charged it will then send some juice to the 2nd one?

Yes, Neg to Neg.

I also wouldn't worry about a second battery unless you are planning on running lots of things with the engine off for prolongs periods of time. I have additional lights, and a winch and just have the largest highest rated battery I could fit in the space and have never had a problem with the battery going flat. Second battery's are ideal for camping setups where you will have lights and fridge etc running when the vehicle engine is not running other than that they are a lot of hassle for every little benefit imo.

dag019 said:

I also wouldn't worry about a second battery unless you are planning on running lots of things with the engine off for prolongs periods of time. I have additional lights, and a winch and just have the largest highest rated battery I could fit in the space and have never had a problem with the battery going flat. Second battery's are ideal for camping setups where you will have lights and fridge etc running when the vehicle engine is not running other than that they are a lot of hassle for every little benefit imo.

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I've been thinking about it and i'm starting to agree with you, i think i want more overall capacity rather then a 'reserve' battery.
I think i just got excited when i saw it was already set up for a 2nd and the fact i have a brand new battery i took out of my old car that was written off.

Do you know what size battery you have?

marc.postle said:

I've been thinking about it and i'm starting to agree with you, i think i want more overall capacity rather then a 'reserve' battery.
I think i just got excited when i saw it was already set up for a 2nd and the fact i have a brand new battery i took out of my old car that was written off.

Do you know what size battery you have?

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I have a 640SHD Yuasa Cargo Super Heavy Duty Battery 110Ah YBX3642 (LINK).

When I was looking at it I found that to fit two batteries in the box you needed smaller batteries (the height is the main limit) which meant that overall there was not a huge Ah improvement and you needed a very expensive primary battery to get a good high CCA figure. The main benefit of two batteries and a split charge is for running things with the vehicle off while still preserving your starter battery (e.g. camping) or you are competing in winch challenges etc and just need huge amount of power. If you do not do this then as far as I am concerned it is not worth the cost and effort. If you already have everything in place and already have a second battery the only cost/effort will be in mounting them so there is no loss to fitting it, but also don't expect much benefit.