Dual battery in P38A

**Junosi** · 14th March 2011, 09:34 PM

Bigger is better is the rule of thumb for the wiring, if in doubt go bigger. I went with gauge 3awg which is 25mm², some go gauge 0 (53mm²) or more . Basically the smaller cable you go the more voltage drop you have and slower the battery will charge, if at all. There's a bunch of voltage drop calculators around - http://redarc.com.au/handy-hints/calculators/voltage-drop-calculator etc.

My used about 5.5m of gauge 3 twin cable running along the left chassis rail.

Also it's always better if you can earth your second battery directly back to to the earth on the primary - chassis etc can't be relied on to be a good earth unless you have to. Use a sealed AGM type battery if you can (rather than a wet type) - primarily because they recharge 3-5 times faster than other types (assuming your wiring is good), they're good in every other way too.

**p38arover** · 15th March 2011, 06:06 AM

Originally Posted by 81stubee

If you have a gas tank, then the spare wheel well is the go. But from my research. If there is to be a battery inside the Vehicle (spare wheel well is inside) then it must be a sealed unit. ie you can't use a conventional car battery in there. Most of the deep cycles these days are sealed anyway.

I have an AGM in mine.

**Keithy P38** · 15th March 2011, 08:39 AM

Thicker wiring will also help in the event your primary battery has discharged and you need to get your car going!

**p38arover** · 15th March 2011, 09:11 AM

Originally Posted by Keithy P38

Thicker wiring will also help in the event your primary battery has discharged and you need to get your car going!

I assume you are not expecting to draw starting current through it and the dual battery controller.

**Scouse** · 15th March 2011, 09:16 AM

Originally Posted by Keithy P38

I was thinking of making a cubby for mine on the opposite side to the stacker/sub unit in the back, although I think that with some minor mods to the battery box i'll fit two in there... Anyone for a triple battery setup :-p

Cheers
Keithy

The 1996 Calvert Expedition RRs had 2 batteries (stacked) where the subwoofer sits. They fitted in nicely, and they were big batteries.

**glenhendry** · 15th March 2011, 05:15 PM

I have bought the battery and the dual battery kit. Final question is where to mount it. I much prefer the thought of under the bonnet as it will simplify the cabling.

I realise that some batteries are specifically contraindicated under the bonnet, but I bought a fully sealed 98AH battery that is fine to install under the bonnet or in the spare wheel well.

It looks to me like if I bust out the battery tray in my 2000 HSE that there will be enough room for two batteries side by side there. All I would need is an interesting tray to hold both as the 'floor' isnt level there. The compartment aft of the current battery is empty as the ECU was moved for Thor engines, so I think I have room for the entire dual battery system and isolator unit under bonnet.

Has anyone done this? Why did all the installs below chose the boot option?

Thanks for any more great input before I bite the bullet and trash my OEM battery tray.

**p38arover** · 15th March 2011, 05:24 PM

Originally Posted by glenhendry

Has anyone done this? Why did all the installs below chose the boot option?

I have seen two fore-and-aft batteries in the underbonnet location on a post-99 model. I thought I had pix.

With the GEMS (like mine) that box contains the engine management system so there is little spare room.

**996TURBO** · 15th March 2011, 06:16 PM

Originally Posted by Scouse

The 1996 Calvert Expedition RRs had 2 batteries (stacked) where the subwoofer sits. They fitted in nicely, and they were big batteries.

What's this vehicle? Never heard of it before.

**p38arover** · 15th March 2011, 06:40 PM

Originally Posted by 996TURBO

What's this vehicle? Never heard of it before.

See Land Rover Calvert Expedition

**glenhendry** · 15th March 2011, 08:24 PM

OK, I am going to go for the underbonnet system and I will document it.

Anyone care to comment on where I connect the positive terminal of the auxillary battery to? In the following two links here and here, the diagrams suggest connecting the aux battery positive terminal to the 'accessories' or 'auxillary load'. For me, I want that to be all of the cig lighters and radio etc. Can I just wire that straight back into the fuse box so all the cig lighters (front and back) are powered by the aux battery when the engine is off. Surely I dont have to run a separate circuit?!

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