Battery Relocation

Yea, do not drill into the tank to mount the box. That would be bad!

The type of box you use could be regulated by the race class if you take it to the track, so check that first. Also, as the trunk is not fire walled from the interior, a sealed box with an external vent would be my choice.

I checked out the sealed kits that are approved by the racing sanctioning bodies. It looks like they have a vent tube to the outside. You would not want the sulfuric acid vapor in the trunk, and you are not to smoke or spark near a charging battery because of the gasses released in the process.

I'd really be leary of installing a battery in the trunk of one of these cars. Ever accidentally touch a wrench to ground and create a spark while tightening the positive connection on a battery? Add that possibility to a car that has a rubber hose going into the fuel tank through the trunk where there very well could be fuel vapor. In my opinion the risks outweigh the benefits for this mod.

I've sparked the battery in my trunk, I'm still alive. People have been installing batteries in the trubk for decades and I've never heard of anyone exploding. They must all die, and there are never witnesses.

I put together my own battery relocation kits. I use 0 gauge ground wire from a welding supply store, I always buy 20' but always have 3 or 4' to spare because I extend the wiring for the starter solenoid and mount the solenoid in the trunk as well. This way, the hot lead from the batterey is short in length. Not wise to run the hot lead the length of the car, what if the wire housing rubs raw and shorts out on the frame somewhere? Also, the long lead goes straight to the starter from the trunk mounted solenoid, instead of to the engine compartment so it cleans up the engine compartment even more. For eyelets, I just buy a short length of copper plumbing pipe, cut as manny ends as I need. I use a vise and flatten one end, insert bare wire into the open end and give it a squeeze with channel locks to keep the cable from sliding out, heat copper with a torch and fill it with solder. Remove from vise and drill a hole into the flat end. I wrap the round end to cover any remaining exposed wire.

I buy a marine application battery box, run about $20. It comes with flimsy mounts and a weak strap. I used to get a ratchet strap and hook one end to the spare tire eyelet, and the other end to a hole I would put into the rear trunk dropoff. In recent years I've just bought the metal battery tie down strap with the 2 long J hooks. I drill 2 holes through the battery box and through the passenger side trunk foor wide enough for the battery to fit between. It comes with rubber washers, washers and wingnuts. I run the hooks from under the car, through the floor and box the the rubber washers. The rubber washers keep the hooks from falling through every time you remove the wing nuts. This all solidly mounts the battery/box in place. You don't want the battery rolling around in the trunk and shorting out. Also, if the solenoid does get trunk mounted, be careful transporting metal parts. I did this once and while driving, of all places to come on contact, a metal part engaged the starter. I run the solenoid to the outer side of the passenger trunk hinge bracket near the wheel well now.

I also have a quick disconnect on the ground wire. I like this, saves time having to tear into the box and remove battery cables.

While being transported on a flatbed cross country I left the battery in the trunk loose. Didn't think it would be a problem. Car arrived hours before I had to be on a plain to Afghanistan. A year later I get home to find this mess out. It left yellow powder, surface rusted the floor a little, dripped on the aluminum in line Aeromotive fuel filter and oxydized it, imagine the ends have fused where it threads together. Also the fuel cell breather valve tube is aluminum running through a hole in the floor, that oxydized and became clogged with yellow powder too, cut the clooged end off. I vacuumed the trunk out. There was no smell of acid but ther was still a dry residue present. I used wet paper towl to wipe it all off. Then I carefully soaked the effected areas using a bucket of water/vinegar solution, then rinsed with straight water and let it wash out. Used an air moving fan for quick dry and added a new coat of paint. Its holding up fine now. Because of this I just went ahead and painted the bare aluminum fuel cell.

Fantastic description. Wouldn't mind pics of this too if you have any.

Late to the party but it's worth mentioning that all Miatas have trunk batteries. Lots of BMW's do too. It's not that big a deal. Since somewhere in the 1990's Cadillac put theirs under the back seats in most of their cars. Keys are to vent them outside to fresh air and to make sure they are securely mounted. No harm in following NHRA's rules for trunk mounts even if you never intend to race as the only purpose of those rules is safety.
Carroll Shelby popularized putting batteries in the trunk for race-oriented Mustangs back int he 1960's. Reputedly relocating the battery to right over the right rear wheel is actually better than completely removing that weight from the car. Drag racers have proven certainly it helps traction at least a little.
You can make a good argument that for the average person relocating the battery is not at all worth the trouble. I like mine in the trunk though.

All 1965 Shelby Mustang GT350's had the battery mounted in the trunk without a safety box. Those vehicles did have acid-vapor problems and later cars included vent tubes running out of the trunk. 1966 GT350s kept the battery in the engine compartment for vapor and cost reasons.

I mounted my battery in the trunk and have not had any issues but I bought a modern sealed-cell battery where it doesn't vent anything.