Battery Relocation Instructions
for a 2003 Subaru WRX

I decided to relocate my battery to the trunk for 3 reasons:

1. I upgraded to an Optima battery, but the post polarity is oposite
of the OEM battery. This means the main power cables would
have to be spliced and lengthend approx. 3 inches.

2. I will eventually be adding an FMIC, and knew
I'd likely have to move the battery anyway.

3. I'm in the process of installing a custom audio system,
so I already had the interior panels removed.

So, with a little planning and some advice, I took on
the project last Saturday. These are the steps I took.

*Note: I am not a professional, nor did I follow any instructions. I just figured it out logically, and everything works perfectly. I am not responsible for any damage to your vehicle or person due to improper wiring.

You MUST use a Gell-Cell or Dry-Cell type automotive battery if you are mounting it within the vehicle. Lead-acid batteries can emit dangerous fumes within a closed space such as a car cabin or trunk.

Parts needed:
18 feet of 4-gauge red power cable
3 feet of 4-gauge black ground cable
1 foot of 8-gauge red power cable
6 4-gauge ring terminals
1 8-gauge ring terminal
1 power distribution block with at least two 4-gauge positions and one 8-gauge position...
( I recommend the Monster Cable compression-style 3/3 fused block )
2 battery post clamps with bolt-down connector
1 100-amp circuit breaker
about 10 inches of .125"x2" aluminum for battery hold-down
1 Gell-Cell / Dry-Cell automotive battery
1 battery tray (Optima brand batteries come with a tray)

Recommended extras:
.062" solder
propane torch
60 amp glass fuse
5 minute epoxy
1/2" vinyl tubing

The first thing, I removed the OEM battery, but realized that I needed to leave the orginal battery connections in the engine bay intact until I was ready to make the final connections with the new setup. (With no electric, nothing in the car works!... like the windows if a quick rain came along.) With that thought out, I started by running the main power cable.

I used 18 ft of 4-gauge red Monster Cable, cut into 3 pieces:
-One red 6" iece for the battery-to-breaker
-One red 16" piece for the distribution block-to-main power splice
-The leftover red length was perfect for the engine bay-to-trunk run.
...and one 3ft length of black 4g cable for the main ground.

I highly recommend running the main cable from the trunk to the engine bay first, and then cutting the smaller pieces from the excess. It's cheaper/easier to buy a few more feet of cable than it is to buy 15-20 feet if you come up short.

I then made all my 4g terminal connections. There were 6 in all. I bought Monster Cable crimp-style terminals, which are sealed at the ring end. You can simply crimp them as they were intended, or use a more permanant method utilizing a propane torch and solder... With a vise, or a pair of vise grips clamp the ring terminal so the cup end is pointed upward. Heat the cup with a propane torch for about 10 seconds, then start feeding solder into the cup, re-heating as needed to keep the solder liquid. Fill the cup about half-way. (It takes about 1-foot of .062" solder.) With the 4g cable stripped about 1/2 inch, heat the bare cable for a few seconds, then put the heat back on the cup for a few seconds as you push the cable into the cup. Remove the heat and hold the cable still for about 30 seconds, or until the solder has hardened. There is no need to crimp. Slip the supplied heat-shrink tubing over a pair of needle-nose pliers and pull apart to stretch the tubing enough to slide over the terminal+cable connection. Heat the tubing with the torch from 6 inches away for about 5 seconds. Bam! A solid corrosion-resistant connection. See Below...

Also, before soldering, I bent 3 of the terminal ends 90-degrees for better fit. See below...

Next, I secured the Optima battery's lower riser tray (photo below: A) to the driver-side floor of my trunk near the jack mount. I used two thick 1/2 inch metal screws in the base, and one more horizontally into the metal brace behind the wheel well. (illustration)

I made a battery hold-down (photo below: B) from a piece of .125"x2" aluminum. I used 5 minute epoxy to secure the circuit breaker's (C) mounting plate onto the hold-down bracket (B). I bought a pair of gold-plated marine battery post clamps from my local auto parts store. The 6" red cable with 1 straight ring terminal and 1 bent ring terminal attaches from the positive battery post to one side of the circuit breaker. The long main cable attaches to the other side of the circuit breaker with a bent ring terminal too. Be sure that you leave the circuit breaker OFF for the remainder of the install. Connect the black 4g main ground cable to the negative battery post.

*Note: I chose to mount the battery so that the side posts are easily accessible. I plan to use the side posts to connect an amp and other accessories. They also allow for a convenient connection for jumper cables, if needed.

The power and ground cables (below: A) are zip-tied together, and run along the bottom edge of the wheel well. Cut a few inches of .5" tubing, split it along it's length, and slip it over the power cable to protect it from the metal edge (below: B, but is not in the photo).

The ground cable (below: B) attaches to the chassis using a bolt for the rear lower seat cushion bracket (below: A). I used a wire brush to scrape away the paint on the floor where the ring terminal touches for a better connection. I also wrapped a short piece of .5" tubing on the power wire (below: C) where it rests against the metal braket edge for protection.

The main power cable runs under the carpet along the driver's side of the car, and thru the firewall behind the clutch pedal arm. Be sure to use the existing rubber grommet, or some sort of protection, to ensure that the power cable's insulation does not get cut by the firewall's edge. Then run the power cable along the edge of the wheel well, to the front outside corner of the old battery tray, and end up behind the front headlight.

Here, I used a Monster Cable distribution block with three 4g positions, and three 8g fused positions. It's more than I needed, but leaves me open connections for future powered accesories. This particular distribution block uses compression-style connectors, so no ring terminals were needed. Connect the main power from the battery (below: A), and the 16" piece of 4g wire (below: B) to the block. This is a non-fused pass-thru connection.

Cut a 12" piece of 8-gauge red cable (below: C). This will connect from the distribution block to the main fuse block/power relay box in the engine compartment. Use one 8g ring terminal for this wire, and connect the other end to the compression-style fuse holder. (I used a 60-amp glass fuse here.) The extra connection points are left open (below: D).

Here is another view of the mounted distribution block, behind the driver's side headlight, on the wall where the OEM battery used to be. (A: from battery, B: to original battery power cable, C: to fuse box)

Remove the windshield wiper tank by removing the 2 bolts at the top (below: A), then swing it up to get it out of the way. You'll need to disconnect the pump wire clip, but not the fluid hose. Then remove the fuse box by unscrewing the front bolt (below: B).

You'll be able to pull the fuse box up enough to get at the underside. Remove the plastic cover to reveal the wire connections. You'll see 1 wire that connects from the original battery post to the fuse box by a nut. (Sorry, no photos of this, but it's obvious.) Remove the original wire, and replace it with the new 8-gauge wire from the distribution block. Replace the plastic cover underneath the fuse box, then secure it and the washer tank back to their original locations. Reconnect the washer pump's electric wires too (green plug).

Now, it's time to chop off the original main ground and power battery post clamps. Here are the peices you will be removing: (below) A: Battery power wire to fuse box. B: Battery post power clamp. C: Battery post ground clamp. Not pictured: The battery ground-to-chassis wire. You will not reuse any of these pieces.

I spliced the original main power cable (black with red stripe) to the 16" 4g piece from the distribution block (photo below: A). I used a 1" piece of copper tubing the same diameter as the 4g cables to connect the two together using the torch/solder method, then crimped the ends for added strength (illustration below) and covered with heat-shrink insulation tubing.

Next, solder a bent ring terminal onto the 4g original ground cable (black with yellow stripe). Attach this cable to the OEM ground point on the wall in front of the fuse box (below: A). Be sure to use the original star washer for a good connection. (B) Is the new 8g wire leading to the fuse box from the distribution block.

That's it!

Flip the circuit breaker's switch to ON.

Start 'er up!


**Additional info for aftermarket engine grounding setups.**
If you are using an aftermarket or DIY grounding package, I advise that you run an additional 4g black ground cable from the battery's grounding point to the new grounding point in the engine bay... or to a grounded distribution block. This will offer a direct ground path from the battery in addition to the chassis ground.

Please feel free to contact me if you have any questions.