twin battery system - Prado

I investigated this many moons ago, so details are sketchy.
The second battery goes towards the passenger side firewall, some movement of canisters etc is required. You can only get a smaller battery than existing, so it is advisable (if second battery is to run fridge, lights etc - not for winching) to use smaller second battery for starting, and the existing (replace with deep cycle for camping power.
I have seen this in several 3.4 petrol Prados.
Thommo

Bear,
If it is a 3.4 Petrol, then I assume that it is a 1996 to 2002 model. Is this correct ?

If so, the best alternative is to buy a cradle kit for the Prado from Opposite Lock (no I don't work for them, just I had a good experience.) I don't recall the brand of the cradle kit, but it fits as follows,

The second battery is mounted in a cradle that sits where the carbon cannister normally sits on the left hand front inner guard. The carbon cannister is relocated to a spot on the side of battery cradle. The second battery in the cradle is the same size as the original starting battery.

There are a number of options, you can fit the existing battery to the new cradle and have the wiring altered to maintain this as the starting battery.

In the place of the existing battey, you can then fit a larger unit, such as a heavy duty 4x4 battery ie 150 ah.

In my case I chose to leave the existing starting battery as is and fitted a Marine Battery (it's Yellow and Blue, can't think of the brand name at the moment) in the new cradle. The marine battery has a Reserve Capacity of 95ah. I only use it to run the fridge.

I used a Rotronics controller (MH10), but there are others that are just as good if you have a preference for another electronic type.

I did the total installation myself and the only fiddly bit was relocating some of the pipework around the carbon cannister, but the kit had clear instructions plus all the bits needed to do the job.

Also, I ran the battery cable from the second battery (through the firewall (via the existing rubber grommet) into the passenger compartment, along the internal sill channels (under the plastic trim) into the rear compartment. Just make sure the lead to the battery in the back is fused at the engine bay end. I used a self resetting circuit breaker for this purpose.

I have run a 8GA cable (6.5 mm), plus a number of other leads to the
back this way, and have had no problems getting it through the rubber
grommet (just undo the electrical tape around the grommet prior to installation of the cradle).

I think the above option will give a much greater second battery capacity compared with what I found at the time where more expensive systems that attempted to mount a second battery next to the original one.

Hope this helps,

Cheers,
Mal58