Battery relocation, trunk or in car? 69 AMX 2 seater.

[813Demon340]

I'm looking for opinions on which is the best place to relocate my battery in my 69 AMX. I can move it behind the passenger seat in front of the rear wheel or move it to the trunk on the passenger side. I don't have a set of scales to see what the difference is between the two places. The trunk will move more weight rearward and farther out, behind the seat will move the weigh lower in the car but slightly inward. Moving weight rearward in the AMX is important because of the 97" wheelbase. Obviously there is no back seat in these cars, there will only be a rollbar. The car has an LS1, 6speed, glass bumpers, and has been on a diet where possible. Here is a picture of my previous stock 68 AMX on scales with steel bumpers and an AMC 390, auto. My car is probably around 200 lbs lighter, mostly in the front. The battery is an optima/sealed battery, FWIW.

So, behind seat or trunk? Or does it even matter? Thanks for the replies ahead of time!

[Vimes]

A typical battery is 41lbs, which makes for an 82lb adjustment front to back. Based on that scale reading and understanding that this is not your car, setting it in the trunk behind the passenger wheel would be best. Plus you really don't want the battery in the passenger compartment without putting it into a sealed box with a vent to the outside. You could put it in the trunk, but even there I'd stick it in a box with a vent as a battery can generate hydrogen sulfide gas, and it doesn't take much of that stuff to kill you, unless you have the trunk sealed off from the passenger compartment. Not to mention, if it gets concentrated at all it just takes a little spark to go BOOM. The gas is heavier than air so as long as you're venting it won't be an issue. You do want to be able to contain acid spills though, don't want that getting on the interior

[Just 1 More]

batterycovers by F G, on Flickr

[Jim Streib]

While I cannot say which would be the best position, I will add the suggestion of putting the battery in a vented enclosure is the best and then also adding in some kind of protection on the main power wire (or any wires for that matter) to where if a short or overload occurs, a fuse, fusible link, or breaker will open up. Do not be confused thinking that a master on/off switch or a remote solenoid will give the same protection. They will not.

Also when doing the wiring, stick with copper wire and stay away from the copper clad aluminum stuff (CCA wire).

Jim

[79 Camaro]

An optima doesn't need a sealed box. I would put it the trunk. If something really bad happens I wouldn't want a battery flying around the interior.
If you go trunk mounted as said above use welding cable. When you route the the cables thru the sheet metal use the isolators that bolt thru the sheet metal not grommets. Run the ground cable from the trunk connection all the way up to the engine or trans.

[Jim Streib]

An optima doesn't need a sealed box. I would put it the trunk. If something really bad happens I wouldn't want a battery flying around the interior.
If you go trunk mounted as said above use welding cable. When you route the the cables thru the sheet metal use the isolators that bolt thru the sheet metal not grommets. Run the ground cable from the trunk connection all the way up to the engine or trans.

You do not want to put any battery in a sealed box. You do though want the battery when not under the hood to be in a vented enclosure or equipped with vent tube nipples that a hose can then be attached to with the vent going to the exterior of the vehicle. Even optima's can vent explosive gases AND all the ones I have seen either have vent caps or spots to connect vent hoses to them. Some batteries have the vents very well concealed but are there.

Optima with vent nipples:




An older style that a customer had an issue with with pressure being released through these vents:




One brand with concealed vents covered with rubber caps:

As Delivered:



Top plastic cover removed exposing vent caps:





Jim

[813Demon340]

Thanks for the replies, I didn't know that about optima batteries having vents. Trunk it is. Jim Strieb's point of it being able to fly around inside is a good one.

[Richard454]

There are millions of cars with batteries in the interior. Thousands mount the battery under the back seat.


Corvettes have been doing it since 68- right behind the driver seat.

Thoughts - lower center of gravity and if the interior is cooled /heated the battery lives longer and its best performance it around 70ºF

Another trick is to mount a jump post under the hood- near the starter- Starter gets full juice and easy to get to.

Richard

[Vimes]

No to a sealed box? Yes and no. A minor, but important point, the box needs to be vented but it also needs to be sealed off from the interior. Hydrogen sulfide gas, aside from being deadly to people in even small amounts, is also highly corrosive. Under a car hood there's enough airflow to vent it away but inside the trunk it will settle into the low parts of the trunk and start eating away at the car body from the inside. It'll take a few years, but eventually you'll need a new quarter panel. You also want that vent to be low on the box, not high. Since it does settle down, a vent high on the box will mean that the battery box will fill with the gas before reaching the vent. In addition to its other fun properties it only needs a spark, like you'd get when pulling the negative cable off the battery, to ignite.

Not a big issue, just use a sealed battery box with a small vent at the bottom, and run a tube from the vent to some point under the car. Moroso makes a nice, simple, NHRA approved one.

[Jim Streib]

How they did some old school battery venting circa 1964:



Jim