Purpose
This has been brought up a few times, and I'd like to start an informative thread on the subject. Comments that do not pertain to the subject will be removed.
Other opinions on technique, correcting faults, etc, are welcomed. If you have done this and have pictures, those are welcomed.
Now,
Battery Relocation, be it for performance, lack of room under the hood, a short run of wire to your amps, or simply because you want a battery back there is something that has been touched upon in this forum and others but we have not had a real say all to what should be done. I'm going to break my post into a few sections, if you have your own input, use whatever format you want.
Safety
First and foremost, a battery isn't something that should just be placed in your trunk / hatch. It has to be secure. A lot of these are filled with acid and can weigh 30 lbs. Imagine what would happen in the case of an accident with this acid filled brick flying at your head? The answer would have to be - nothing good can come of something like that, which isn't secured properly.
There are several kits out there for battery relocation. And i say most of them are fine, but we can build a better one ourselves, if we know how. and probably save a little money in the process. The battery box is something that is necessary for ANY acid filled battery. This box bolts to the floor of the vehicle, and i recommend using large washers underneath to spread the load so the nuts wont pull thru the floor in case of any accident. Now we have a box bolted down. If you have an acid battery you'll need a vent. You can punch a hole thru the bottom, then insert a hose, seal up around it, etc. This should work fine. (in theory) The battery needs to be held down. Most autoparts stores sell universal kits to strap them down consisting of some threaded rod with a 90* bend on the end. These work fine but can fall straight down when you pull the battery back out and can be a bitch if you are trying to install a battery. Normal threaded rod with a nut/ washer on each side of the box (ie, outside the car, inside the box) might be a better option. Who knows.
That being said, now we have our location for our battery, and the battery and box securly fastened to the car. I'm only going to touch the next part once, assume it for every hole we drill - rustproof the damned thing.
Fusing
Our oem alternators put out something like what, 140 amps? When i measured starter draw on my car with an ammeter, i got 39 amps. With these two numbers we can size our fuse. I would think that anything over 140 amps should suffice. 150 would be fine. Make sure you place your fuse within one foot of the positive terminal on the battery. The closer the better. I believe mine is 6". Note: XR alternators aren't as powerful, but the starter draws more current. I recommend a 200a fuse for XR's @ the battery.
Sizing Wiring
Another possibly touchy subject is proper wire size. Many people say 0/1, some say 4awg is fine, and some go with 2awg. In my focus I use 2awg from the front to the back, then a 2awg and a 4awg for ground. (to the same point). Given the fact the starter draws only 39-45 amps, 4awg should be fine. Given the fact the alternator could theoretically put 140 amps thru the wire, 2awg is a better choice. Honestly i think 4awg should be the minimum sized considered. And bigger is better, unless you're building a pure racer and care about the extra few pounds of weight you're gonna get. Your call.
Running Wiring
Okay, now we have our box mounted, our battery strapped in, our fuse placed, and our several feet (16 should be more than enough) of large gauge cable sitting next to us. Where do we go? Well, front to back, right? I would start from the center of the car. Pull out the driver's seat. (T45 and T40 bolts, IIRC). Pull out the seatbelt rail on the side bottom. Remove the kick panel, and the lower scuff panel. remove the rear seat bottom, and if you want, the upper part of the seat back. Then remove the B pillar panel, then the quarter panel piece. Sounds like a lot of work, but will save you a lot of time. After you've done this once or twice you can get all this out in 20 minutes.
Okay, now pull up the carpeting (4 plastic clips under where the scuff panel was). Fold the carpeting up and back out of your way. Imagine where you are going to run this wiring. Now, if you bought cheap wire here is where you will pay. Most low strand cables dont like to bend. And you're gonna need some flexibility here. I've found knukonceptz cable to be very high quality and a great price - (shameless plug) that is VERY flexible.
Locate an area on the firewall to drill (this is how i do it, if you have a different way, post up). I tend to use the area above the clutch pedal, and about 1" below the green tab. This brings the wire out under the fuse box. After you drill the hole, deburr it, then rustproof. Insert the grommet, and feed your wire thru. Having a friend at this point can help route the cable, but you can do it on your own. Figure out where you want the cable to end, then seal the hole (excess in the grommet) with RTV / silicone / etc.
Now go under the hood and secure the wire with cable ties in the desired location. You already know not to attach it to things like your shift linkage, i hope. Keep it simple and away from any moving parts. Remember - your tranny mount moves. It will wear a wire thru if you just simply rest it on there.
Route the wire to the rear of the car. At any point where the wire has the slightly chance of chaffing, protect it. Wrap it with tape. Wrap it with split loom, do whatever you have to do. Secure the wire at regular intervals. Also please keep mind to the size of the cable you are running and where the carpeting lays. If you put it above the seat supports, you might have clearance issues. If you put it near where the seat bolts down you, you might have some issues with pinching it. Avoid these situations. You'll see where the factory wires run towards the rear. You can follow those except where it goes above the seat rails (in my opinions). Also PLEASE do not run the wire under where the rear seat folds down. This will chaff the wire thru. Especially a large gauge cable.
Bring the wire to the back of the car and secure it as necessary.
Putting it all together
Alright, now we've got a wire under the hood that goes to the back of the car near a battery box that has a fuse near it. All areas of the wire are protected, and it's not near any moving parts or sharp edges. The wire is at no point bent in a tight radius, nor looped in some ridiculous pattern.
How do we connect it to the factory wiring? Well you have a few options. What i like to do is use a ground distribution block (read - unfused dist block) and cut the factory wires off the factory battery terminal, then insert them into the block (tinning the wiring helps keep it secure). Then all you have to do is insert your new battery wire to the same block and voila.
What about the ground? Well, that's more of the same. I used the factory ground wires and grounded them to the front frame rail, using a bolt that used to hold down the battery box. I polished the metal CLEAN (ie, didn't use a dremel and scratch it all to hell), then crimped, soldered, and heat shrunk a lug onto the wire. Tightened the bolt, then protected the surface with electronic clear coat.
I would also recommend the use of some extra wire to run a few more ground cables under the hood (ie, frame rail to motor) if you have any.
Now all we have to do is connect the new battery wire to the fuse block, put on our ground cables for the battery (you can use any THICK metal surface that has a good ground to the engine. Where the rear seat belt bottoms bolt down is a good choice. Where the spare tire bolts down is a good choice for length of wire as well. Again, protect the surfaces after you sand clean and install the cabling.
Now, for the test, before we reinstall the interior. Go over everything you just did. Make sure all wiring is secure and where you intended it to be. Install the battery terminals on the battery, with the wires connected, and install your fuse.
If for some reason the fuse blows instantly, you messed up. Go over it again and correct any mistakes.
Once you have all the wiring installed make sure everything works as it's supposed to.
Few pics of my XR's relocation:
Here is the battery, which is located behind the passenger seat. You can see the ground wire (grounded to the seatbelt slide rail bolt), and the main power wire, fused with a 200a ANL fuse.
Here is how the power wire is secured - self drilling screws with cable tie clips, and cable ties, every 6".
not the most recent, nor best pic of my distribution block, but it gives you an idea.
i'll have to take another when the snow melts off the car cover.
