I'd like to relocate battery to trunk in my '89 Diplomat AHB. Obviously, there won't be a kit out there specific to this model. Any recommendations on generic kits, and other tips? Also, do I have to buy a Gel or AGM, and does the battery have to be vented? Right now I have a big wet cell Interstate.

Thanks.

Larry

Never used a kit, just amassed what I needed of it wasn't already on the shelf.
I would think your car is essentially the same size as a B-body, if you prefer a kit.
The archives should have several trunk-mounted battery threads, holler back and I can go into detail if needed.
If you don't need a kill switch it's really simple, heavy gauge wire is the concern.
Vent a wet battery outside the car.

I've seen a couple that used vented marine battery boxes similar to this. Yes, you want to vent it.

Vented Marine Battery Box

One easy way to vent modern batteries is to use the small vent ports on many sealed batteries. GM puts some of theirs under the rear seat. Many including BMW does not use a sealed box, just vent tubes.

Also one thing I did Iearn the hard way is make sure your negative cable is at least 1 to 2 sizes smaller than the positive. Event the factory does this. When a worst case scenario goes wrong & the positive cable gets grounded through a short at the firewall or starter when you crank the engine, you want the short ground in the trunk to burn not the 20 foot long positive wire running the length of the car.

Here is picture of a vent tube and therre are several styles. GM's are oval.

I would use the Ford starter solenoid and set it up so that the wire running to the starter is only energized when the key is in the start position. Something else to think about is if you ever run it at a track then you will be required to have a remote kill switch that is accessible from outside the car. I think the small and light lithium car batteries are down to around $300 now though. Might want to consider going that route and build a smaller battery tray in the stock location.

something i have wondered about....... if the factory put the OE battery in the trunk or under the rear seat, do you STILL have to have a remote cut off ?
i have seen many a new challenger running down the track without.
and if it is legal for them to be without, why ?
i understand the safety aspect completely, but if a car gets tech'ed and the workmanship is good, how can a relocated battery be any different than OEM ?

I relocated my battery to the trunk, put it in a NHRA approved box and discovered that the battery is puking acid in the box and it's dripping out around the hold down bolts. The car has a Powermaster GM one wire alternator and according to them is functioning properly. Now I need to rethink my battery selection.

The cutoff is required if you relocate it. If the car is factory with battery in rear, not required IIRC.

For the OP, make your own cables or have them done by someone. The kits usually don't have the stoutest wire for the project. Additionally, there are other issues to consider when placing the battery in your trunk. If you aren't going to nhra race the car, no cutoff is needed. Some use that cutoff as a theft deterrent. There is always the minimum standard and improvements from that standard.

I agree, but I had a starter work loose during a race. Went to start he car up later and boom lit up the negative cable like a Christmas light. If I had sized them both the same I probably burned the whole car when the 20 foot long positive wire lit up too.
The starter solenoid method is good but doesn't prevent what happened to me.


Instead I put the starter back on and replaced the negative cable. Back in business.



I agree. I do know the positive wire on the new Charger's feel an awful lot like a fusible link. The cover is more rubbery and less like plastic. It runs inside the car too so.....hmmm

That sounds like it's overcharging the battery. Even though it's a one wire alternator it has to get a "Sense" of the voltage in the system to regulate it. If it is thinking the voltage is low it will crank up and overcharge your battery and still test fine on a bench tester.

Check your voltage and see what it is at the battery and alternator when running and shut off. I may be wrong but I think it will be too high at the battery when running.

Must be vented. I see no reason for a small gauge negative cable, except it has less length. No manufacturers I know of shut the poistive power off with a solenoid. Use the bggest cable you can get . Welding cable works well. The area behind the trunk at the back seat should be sealed with metal . NHRArequires a rear accessible shut off switch in the positive circuit. Though street use not necesary. NHRA also requires 3/8" battery hold downs. Dont forget to reinforce the floor area under the holddowns.
Doug

It tested 14.7-8v at the alternator at idle and 14.8 + at I'd guess 4000 rpms, at the battery it tested 14.5-6v at idle. When I called Powermaster I gave the tech the p/n for the alternator and asked what the idle output should be? after telling him what size pulleys I'm running he said 14.8v. Then I gave him what my voltage readings were and he told me that my charging system was working perfect.

That shot my first inclination down.

What kind of battery?

Deka 1000 CCA group 24 lead acid marine starting battery.

You can use the method that used to be circulated quite a bit, and that I used, where the main thick positive is only ever connected to power (and therefore live) during cranking (it's only the starter that needs that amount of current). The rest of the time it's effectively disconnected and everything is fed by a much smaller cable that is fuse protected. So no chance of ever lighting up your cables

Some good info thanks. I'm going to take a real close look at my Charger police battery setup. Of course that's boxed and vented and setup from factory for in car. I've never seen one of them have an issue. I think I will forgo any kits.

To clarify what some are saying regarding having a smaller ground cable for protection,
currently using 2/0 on both, (welding cable) the ground on our trunk battery goes to the rear frame rail
beneath it,(tied frame) the power all the way up to a junction we made on the firewall.

So should I reduce the size on the short ground cable? and to what extent?

Thanks, Joe

The factory reduces the shorter cable by at least 1 gauge on the cars I have measured. I prefer 2 sizes smaller.

There are a lot of naysayers who claim it's not important but when my starter wire grounded I didn't know it until I went to start the car. It saved my car.

Some people claim they are safer riding a motorcycle without a helmet too.

In your case since you are using 2/0 cable I would run nothing bigger than a 4 gauge short cable. Even a smaller ground won't help if both wires are so big they will not burn before the battery explodes. In an ideal wiring your ground wire should be the minimum size needed to start the car and the extra size of the positive is insurance against that worst case scenario.
After it's cranked you only need a 10 or 12 gauge positive wire for most cars to run on, so the 4 gauge is plenty if it cranks OK.

That should be a good battery for the job. When I first see acid spillage it's usually because overcharging or overheating is boiling the battery acid. In the trunk it will not be overheating.

When I looked up your battery the pictures I saw made it appear to be sealed (no removable top caps) and vented with the GM style oval vents.

If it were me. I would do the following.

1. Hook up a Voltage meter and check for voltage going over 15v while driving and racing if that is your application. Bench testers do not spin an alternator as fast as driving/racing it will.
2. Hook up an ammeter and check the flow of current. It should be near to nothing once the battery is recharged after starting.
3. Hook a vent tube to the vents and place that tube into a jar to see if the acid is coming out of the vent tubes or possibly a crack in the battery.

Definitely a little puzzling because you seem to have done everything correct.

Just to muddy the water a bit

An electric circuit consisting of a source of DC power and a wire making a complete circuit is required for DC electricity to flow. (See DC circuits for more information.)

A flashlight is a good example of a DC circuit



Current shown flowing opposite of actual electron movement
Although the negative charged electrons move through the wire toward the positive (+) terminal of the source of electricity, the current is indicated as going from positive to negative. This is an unfortunate and confusing convention.

Ben Franklin originally named charges positive (+) and negative (−) when he was studying static electricity. Later, when scientists were experimenting with electric currents, they said that electricity travels from (+) to (−), and that became the convention.

This was before electrons were discovered. In reality, the negative charged electrons move toward the positive, which is the opposite direction that people show current moving. It is confusing, but once a convention is made, it is difficult to correct it.

MORE CONFUSION??? HERE