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Move It! How Battery Relocation Works

One of the main reasons to move the car’s battery from the engine bay into the boot or the cabin of your car is to make room for engine mods. Battery relocation can also help with weight distribution.

Before you start ripping the battery out from its original spot though, here are a few things you need to know.

Let’s start with the basics

The car battery’s job is pretty simple: it supplies 12 or 16 volts to the car’s electrical system in order for the starter motor to function, which gets the engine running, which turns the alternator, which charges the battery.

What happens if the alternator doesn’t charge the battery? It goes flat. If your battery is flat you won’t be able to start the engine to get the alternator spinning which you need to do in order to charge the battery – so you’re stuck in a loop of the car not running.

As well as supplying power to the car’s electrical system the battery also filters the electrical system. The charge coming from the alternator can be noisy and often struggles to supply the huge instantaneous current required so the battery also acts like an Electrical Surge Tank.

This means your wiring needs to be right and you need to make sure all electrical devices in the car have good access to the battery’s power. You also need to ensure the alternator has a good connection to the battery in order to keep it charged.

The right kind of battery

Make sure you have the right battery for your application. It’s worthwhile to check with your local Racetrack or Governing Body as they may have specific rules on battery mounting positions, battery types and battery enclosures.

If you’re mounting the battery inside the passenger compartment it should be a fully sealed Dry Cell style battery (regardless of the regulations).

If its being mounted outside of the passenger compartment we still recommend a Dry Cell Style battery.

Normal Lead-Acid style batteries can certainly be used but they require an externally vented battery enclosure and have a chance of leaking nasty Hydrogen Gas and Sulfuric Acid if it all goes pear shaped. It’s always a good idea to use the best and safest battery for the job.

Next, choosing the right sized battery, in my opinion – the bigger the better! If you have the space and you can afford to carry a few extra kilos then go big – there’s no downside!

Where to mount it

When fitting a fully sealed Dry Cell battery remember that mount will need to hold up if the car is ever in an accident the last thing you want is the battery to come loose and go flying through the passenger’s compartment.

There’s plenty of solid, billet mount kits available, shop around and make sure to secure it into a solid part of the car, as low as possible.

How to wire it

Once you have the battery mounted it needs to be wired in and this is where most of the problems happen.

Keep it simple and do it right! You don’t need to add 50 ground straps, just a simple copper thick gauge (something like 0 gauge) ground cable that goes from the negative side of the battery to the block, and from the same position on the block to the strut tower. Take a look at your daily driver, it will be done in exactly the same way.

The problems start to arise when you ground the chassis in the boot then assume the rest of the car has good grounding – which is often not the case!

We use copper wire because it’s a great electricity conductor. Proper grounding is not as simple as finding the first convenient hole and using whatever bolt will fit to screw it down. The 0.8mm sheet steel in the floorpan of your boot with a tech screw holding the ground cable down just won’t cut it. It might work for a little while, but sooner or later it will cause trouble!

Just like the Negative side, the Positive side needs to be simple but solid. The battery cable should go from the battery to the starter motor using the same copper 0 gauge wiring, and from the starter to the power distribution stud and alternator charge terminal.

You don’t need 0 gauge for this. 4, 6 or 8 gauge will do, depending on the electrical demands in the car. Remember that this wire will be LIVE so route and protect the wire so it will not be rubbed or chaffed through.

You may want to fit a circuit breaker to the battery positive cable close to the battery, so if the worst does happen the battery cable will be cut off from the battery. For that you will need a breaker capable of supplying enough current for the starter motor which could be a few hundred amps.

While you’re at it this would be a good time and place to fit a battery Isolator or Kill switch. This is typically a four pole switch which has two big terminals and two little terminals.

The two big terminals go inline with either the positive or negative battery cable, while the two little terminals are used to disable the alternator charge, or “kill” the engine management system.

This way, when the isolated switch is turned off the engine will turn off too, and won’t be able to run solely off the alternator’s output voltage.

Testing the correct functioning of this switch is commonplace at most motorsport scrutineering so make sure to do it right!