The Adventures of Harry

Battery Relocation + Spare tyre delete

This covers the battery relocation I had done on my AW11 MR2 MK1 from the engine bay to the frunk. There are a few reasons why people do this modification, the main reasons being to put a bit more weight up front to balance the car out and secondly to clear up more room in the engine bay. I will apolagise in advanced, I did not intend this to be a pictorial so the images are a bit lacking. Also keep in mind you will lose your spare tyre through doing this, I will be revising this later with an odyssey battery and returning the spare when funds permit.

The modification is pretty straight forward with little to no mechanical knowledge really being required.

Required Items

Small sized battery box, I got mine from a boating store for $15
A Battery Killswitch, I got mine from the same boating store for $17
6 Large Ring Terminals, 3 black, 3 red
3 Meters of RED 2 gauge wire, 1 meter of black 2 gauge
New battery terminals
A fuse and fuse holder, Ideally you should calculate what amperage you require, many people are running 100A however a few have reported them blowing on cranking. I went with a 125A fuse, I am running stock setup shy of a small 4 x 55w amp
Some metal brackets
A strap designed for heavy loads, a basic ratchet strap will do the job here
Random screws and nuts
Cable ties and some heatshrink

Start by jacking up the car, preferably at all 4 if possible and make sure you use proper stands!

First thing I did was I began running the wires into the engine bay from the frunk, this way my car was still drivable if I needed to go anywhere or get some parts, I ran the power wire through one of the gromets in the frunk for the airconditioning (you will NOT need to run an earth wire), easiest way to do this without removing the gromet was to straighten out a piece of coathanger, wrap one end around the wire and pierce the rubber gromet with the other end. At this point feed it through until you cant push the coathanger through anymore, once you’ve done this you will need to get under the car and feed it through, it will most likely foul on one of the AC lines if you have AC.

Pull the cable through from the bottom of the car and start removing the underbody plastics. I ran mine along the underside of the fuel tank with the AC lines, make sure you cable tie it off to make sure it cant come loose and ensure it wont foul on any of the handbrake components. When my cable was routed into the engine bay it came up just near the charcoal canister, this is probably the most time consuming and most painful step of the install.

Now that you have a positive feed from the frunk to the engine bay you should start on setting up the battery box and earth lines. I cut some holes in my battery box and mounted the kill switch on the top of the box, its nice and accessible here for any emergency situations.

Setup your Get out your ring terminals and cut yourself a small piece of 2 gauge wire 10cm max, and terminate one end, this will connect to the large lugs on the bottom of the switch, put the unterminated end into your fuse holder and find a suitable location to mount the fuse holder too on the underside of the battery box. Make up another small lead and put one of your new battery terminals onto it, this will be the positive feed onto your battery, now terminate your positive lead that you just ran to the engine bay with another ring terminal, this will later attatch to your killswitch. If my directions arent too confusing it should go Battery + > Inline fuse > Kill switch > Positive lead to engine bay. You will also now need to make up a negative lead, get approximately 30cms of your black 2ga wire and terminate one end with one of your ring terminals and the other with another of your new battery terminals, this lead will run from your battery to your chassis and it ESSENTIAL it has a good solid earth. There are a few bolts in your frunk that you can undo and then put this lead under however you will need to go to one that goes directly to the chassis, once you have chosen your location sand back the paint under the bolt hole to reveal the bare chassis metal, this is essential for a good earth. Now bolt this earth lead through nice and tight ensuring there is good connectivity.

Now do a test fitting of where you would like your battery box to be situated and take measurements for where you will be placing your brackets, you do not want the brackets to far out from under the battery box, ideally the strap will be coming out from almost directly under the battery box, this will ensure the most secure installation with minimal ability for movement. Once you are satisfied with your mounting system drill through the bottom of the frunk to install the bracket mounting bolts. See mine below, they dont have to be perfectly straight, as long as they are secure and will fit the ratchect strap through, mine are far from however it was a rushed install. Make sure you run your strap through before you tighten these down, ensure you do not use the flimsy brackets and strap that came with the battery box. These might be ok for a boat which is midly swaying but definately not for a car with the orientation of an MR2

At this point if you are happy place the battery box into the frunk and return to the engine bay.
Now we need to connect the two positive leads and the negative, get 2 of your red ring terminals, cut the battery terminal off the original battery lead and terminate it with the ring terminal and also the new battery lead you have just run, using a large bolt and nut secure these together very tightly, also ensure to heatshrink this connection to ensure it does not short out but also to add some added security. You will also have your original negative line from the battery now, once again cut the battery terminal off, and terminate it with a black ring terminal, now you are going to do the same as you did in the frunk, find a suitable place on the chassis to bolt this to, you should have a few spare places readily available and shouldnt need to drill, also as before ensure you sand back a bit of the paint to the metal so you will have a solid connection. You should be able to see my positive and negative leads in this picture

You can also see this frees up a whole lot of space in the engine bay, moreso if you cut out the battery tray. At this point your ok to remove the battery and place it in the box you’ve just installed in the frunk, turn your kill switch to the off location and connect all your positive terminals. After this is all connected connect your negative terminals, then double check all your connections are not going to short, turn the kill switch back to on and crank your car.