Battery Relocation

Why do I want to relocate my battery?

What is the benefits of the above?

Where can I put the battery?

I have seen the battery and air box "swapped over", specialist sealed batteries located under passenger seat, in the passenger foot and also in the boot. Personally I think the best place for the battery is in the boot.

What's the pros and cons of those locations?

Battery and air box swap

Specialist sealed batteries stuck somewhere

In the boot

The best place in my opinion.

The rest of this article only covers locating the battery in the boot.

What do I need?

Hmmm - battery box?!?

You need a method of securing the battery in the boot to stop it falling over or moving around. Demon Tweeks make a plastic battery box. Not seen one in the flesh so can't comment on how good they are. I made one from Plywood covered with blue carpet!

Battery box Lid removed

I secured the box by welding a nut onto the floor pan and bolting it down. Self tapping screws would also do the same job. Caution the petrol tank is below - look before you drill!

I made the dimensions just a little bigger than the box to ensure a snug fit, and then placed a strap over the top to keep everything where it should be.

Drill a couple of holes in the side of the box large enough to let the cables and crimps easily pass through. These will also act as breather holes should any gases be produced.

As the box is a snug fit I also fitted a carrying/lifting handle around the battery before lowering into its new home.

What size cable?

Firstly, if in doubt go BIG - get a large diameter cable. Big is beautiful.

The starter motor is rated at 1kW. Doing a bit of maths (boring) shows that the current drawn by the starter motor is ~85 amps.

Therefore, you need cabling that at the very least carries 85A. Try vehicle wiring products they list 3 sizes of battery cables. I didn't get mine from these people but I did get the 40mm2 cabling...their biggest.

40mm2 cross sectional area cable

What if I get the cable size too small/wrong?

Starting the car draws the most current. If the cable is too small then it will begin to heat at a fast rate, increasing the risk of a fire. This will also make the car turn over slower and make it harder to start. Also, once the car is started then as the cable is too small the current flowing from the alternator to charge the battery will fall as the cable has a relatively high resistance... This is because the resistance of the cable increases with the reducing cross sectional area - in English, smaller cable bigger resistance, less charging, more heat, more danger.

Why do I need a fuse?

Okay, you've run your cable, stuck the battery in the boot, the car goes better than before - everything is marvellous.

Over a period of time your cable may start to rub or chaff on an exposed metal corner/weld etc. As the chaffing continues it will wear through the insulation of the cable until it reaches the inner conductor. If the conductor touches the metal then the positive side of the battery will be directly connected to the negative side of the battery - very very bad. If the battery doesn't explode or catch fire, then the cable will heat to ridiculous temperatures. The cable will heat and maybe set fire to the carpet. You'll have big troubles putting the fire out as you'll need to disconnect the battery and lift up the're gonna need a new car.


What sort of fuse do I need?

I have installed a couple of fuses. One at the battery and one at the cable joint in the engine bay.

The battery fuse you can obtain from RS, part numbers:

342-0205 - Bracket
342-0198 - Insulating nut (buy 2 or 3 as they crumble easily)
337-7959 - 150A fuse

Fuse at the battery


Fuse in the engine bay


Maplin's circuit breaker - 100A. Part No DR92A. I haven't installed one of these...

Engine bay fuse can also be obtained from RS, part numbers:

431-6876 - Fuse holder
431-6747 - 100A fuse
431-6753 - 125A fuse
431-6769 - 150A fuse

Anything else about the fuse?

Get spares. If you try and start the car when it is in gear and you haven't got your foot on the clutch then you'll easily pop a 100A fuse. Carry spares you might need them! I think it is advisable to buy a couple of each fuse listed above, just in case you find you need a slightly larger fuse for your car e.g. starting your car in the depths of winter may take a little more current... I have been running with a 100A engine bay and 150A battery fuse for 6 months with no problems.

What's the best route for the cable?

Poke it through the big rubber boot top right hand side of the engine bay. Down behind the glove box under the carpet across to the passenger side kick plate. Down and along the sill up over the seat against the plastic trim. Then along the metal cross member by the fuel pump. Then back into the drivers side of the boot by the jack.

Have you got a few pictures of your installation?

A step by step guide...

When running the cable avoid sharp corners, burrs, weld marks and anything else that is remotely sharp.

Completely disconnect the battery. Remove the battery, securing bracket and plastic tray
Mount your engine bay fuse somewhere. I had previously fabricated a plate to support the fuse box. I simply bolted this onto the side of it. This will conveniently connect the existing wiring to the new wiring via one of the fused links you got from RS. 100A fuse is suitable. It's also a handy place to connect up other items to 12V e.g. Water Injection
If I 'remember correctly' the negative of the battery connects directly to the chassis and to a starter motor bolt. You'll need to cut this wire and connect the starter motor bolt directly to the chassis as shown here - the red lines indicates the path of the earth wire
Take your cable and run it through the big rubber connector on the back right hand side of the engine bay. This brings the cable out above and behind the glove box
Next clear the route for the cable. Remove the glove box to gain access to the cable you poked through. Also remove the passenger kick plate. Remove the rear seat. Fold the rear seats down and lift up the carpet in the boot. Remove the wooden "thing" bolted above the fuel pump.
Carefully run the cable over to the left towards the door.
Lift up the carpet and run the cable down next to the sill. Cable tie this as you go. Cable ties will help to stop the cable moving around and chaffing...
Feed the cable along the edge and under the plastic trim next to the rear seat and then along the metal cross member by the fuel pump and then backwards towards the jack. Don't forget to cable tie as you go
Remove the plastic trim covering the jack
Remove the jack and the jack mounting plate
Mount your freshly made battery box tight up against the plastic trim. Cut holes in the side of the box before mounting it so that you can pass the cables AND crimps through!
Install the battery in the box. Connect the negative to the bolt directly behind the box and also to the battery. Make sure this is an excellent connection - no paint between bolt and chassis! Then connect up the positive to the battery via the fused link. You'll notice that there is a vent next to the rear light cluster, so any gases produced will be vented out through here
To test everything is okay remove the coil to distributor lead and turn the car over a couple of time for ~10 seconds. Have a feel of the cable. Is it hot? If it is then get a bigger cable

Anything else?

Get the cable crimped professionally. You'll probably need hydraulic crimps if you fit the size of cable I did - 40mm2. I cannot emphasise enough how important it is to run the cable correctly and to fit at least one fuse.

This article was written as a helpful guide as to how I relocated my battery. This should only be performed by a qualified mechanic/engineer. If you are in any doubt or not qualified then don't do it. Altering the design of the car from the manufacturers specifications is not recommended.

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