Relocating battery to trunk

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

Exactly what Powermaster are you using? I see they have a version with an adjustable voltage regulator. As to voltage, 14.8 seems a little high.

The acid is definitely coming out the vents. The voltage tests I did were with the engine running at idle and probably 4k rpms.

I'll have to check the p/n, its a cs121 gm alternator. For some reason 6030 comes to mind, I'll double check though.

That would be helpful. As a note, I tried to find the battery you are using and the closest Deka I could find in a group 24 marine starting battery was part number 24M7 at 800 CCA.

Make sure and use more than one ground strap from the battery to the body, I would run one #2 from the neg. post up to the block or tranny also

Well I missed the p/n on the alternator, it is four digits, so I did get that right.

This intrigued me so I sent an email to the Deka tech line asking about allowable charging voltages for the 24M7 and here is the response:

"Good morning, the operation should be 12.6 - 12.8 , when is charging 13.5 - 14.2"

From this I think you may be overcharging your battery. You may want to check with Deka yourself as I could have misrepresented something.

You may very well be right, it was my first thought too, just not thinking about the battery not being able to handle the voltage, but the alternator output being to high.
It appears I need an automotive type battery.


Thanks.

I'm not so sure that an automotive battery is the answer. 14.8 volts is a fairly high charging voltage. I would recommend you review the following document.

A GUIDE TO BATTERY CHARGING

An excerpt from that is "Although a battery is called a '12 volt' battery, its voltage varies from about 12.6 volts down to 10 volts when it is discharging and can rise to 15 or 16 volts during charging. It is very important, however, to limit the maximum battery voltage during charging otherwise the battery will be damaged. The battery voltage should not exceed 13.8 volts for long periods and 14.4 volts for short periods (8 hours maximum)"

13.8 TO 14.2 is what i was taught, anything over 14.5 is starting to get a little ti high IMO. one has to make sure grounds, accumulative V drops or the V regulator are not what's
over driving the charging rate

I like the Ford solenoid in the trunk idea too. It will make the heavy starter wire dead until cranking. You will then need to jump the small to big lead on your starter.

To be NHRA legal, you will need to cut the charging system with a switch at the back of the car. I have done this a couple times in the past by running the charge wire through the switch but you lose alot of charge voltage running the wire the length of the car twice. If I was to do that again. I'd use the switch to interuppt the field circuit.

be careful switching on and off an alt. field, it can act like a coil inducing a voltage spike on your ignition circuit. There is right and wrong ways to do it. Guess which way I came up with.

Would it meet the Regulations to disconnect the power output of the alternator by de-powering a relay at the front of the car from the switch at the back of the car? It would just be matter of getting a high amp relay.

I do not know if it would meet specs.

So you all are saying a gel car battery needs to be vented also? I`m asking because I don`t know. What about the ones that are sealing the small gel battery inside a old resto battery case like others here have done?

I believe so. The factory battery in my Charger is a gel I believe, and vented.

I scrolled up and I guessed which way you came up with but still do not know.

I have a switch on the alternator field circuit on my race car. With the ignition on if you throw the switch the indicator light I have on the switch flashes very bright, and you get whacked on your finger. I'm no electrical eng. but it has to do with a DC inductive field collapsing like a coil, the winding are the alt field winding.I could probably wire it differently(than the way I came up with)but we just don't touch the switch anymore. It's ok to turn it off and on before the ignition. But if you turn it off with the field energized you get whacked.

I recommend a Transorb or other transient surge suppressor to snub the overvoltage spike...
https://en.wikipedia.org/wiki/Transient_voltage_suppressor

i was strongly considering relocating the battery to the trunk of my charger, but seeing the inner fender under the battery tray is crusted up because of battery acid and gasses, thus needing repair, i'm now thinking i will modify that area for one of those light weight tiny AMG batteries.
.

Hopefully the box will protect any type of leakage. I really want the weight transfer. I didn't know the AMG batteries were that small and light weight.

If the battery is bolted down per NHRA you will have to drill through the box and if your battery leaks or vents acid it will leak around the bolts that hold the battery down. Mine did.

Oh my gooooness ... butt crack Bob with acidic and flammable gasses ? !!

And larryLOVEit..... you haven’t got that done yet ? .....

Forgive me fur asking.... I realize yer very tIrEd !

Nope. Just finished frame ties on AHB! Loving those. Just finished the fiasco of changing out headlight adjusters on Power Wagon. PITA. Change oil on Charger. Oh yeah, and working 50 to 60 hour weeks.

P.S. A big thanks to MarkZ for his excellent fab work making the frame ties come true on my AHB!

Always did this in my race cars. My current street car was under consideration for it and I browsed around and nabbed a few different style of wiring diagrams for it. Since I work slow as a five day fart, I never got it finished and eventually decided to abandon the whole remote idea for a 17# Braille battery in the stock location sitting in a custom tray and hold down. Doing this eliminated a mess of wiring changes, battery box mounting and venting, remote disconnect mounting and the resulting body modification required for remote access to the switch, and rear seat firewall fabrication.

If your interested, here are diagrams:

Thanks TC@HP2.

I really want that weight transfer to right rear.

Why? it is kinda a PITA and if you don't need to why bother? You will also have to put an on/off switch at the rear bumper if you plan on racing anywhere.

My Dart is a street/strip deal that runs in the mid 6.20's in the 1/8 and knowing what I do now I wouldn't do it again. Starting from scratch maybe, but for me it wasn't worth all the work and expense.

Why do I want better weight balance? Better handling, better traction (no, I'm not going to race but for the street traction is good too, especially when it's wet!). Has sure-grip rear, but I like to run fairly stock size tires, 235/70/15, and with the torque my engine makes, I can use the weight back there! And I won't need the kill switch.

Why is it that much work? I see some really nice kits out there on Summit and Jegs. Quality ones. Yes pricey, but that aside, is it really that much work?

larry ... I see ur not LUVIN this frustration

I know of a who lives on the BESTest coast of Florida who would take that PITA off your hands for a tidy sum !!

What you are talking about doing, putting a battery in the trunk, is now totally obsolete. Get a 5 lb, 4" x 5" x 7" lithium battery, mount it up front, or under the car in the inside of the frame rail near the starter. You save 20+ lbs of cable, 50 pounds of battery, reduce complexity, and its cheaper in the long run. Because it lasts 10 years and less wiring cost.

This little Anti Gravity battery spins my 13:1 Hemi over like the plugs are out of it:
https://www.amazon.com/Antigravity-Batteries-Lithium-Motorsports-Battery/dp/B06XKQNJXY

I don't mean to drag this on, but I'm not familiar with lithium car batteries, and tried just reading a bit. Clear one thing up please. Are they also known as AGM's or completely different technology?

I'm liking the 5 lbs! I see I'd need to buy new battery charger. Reading more about them.

Yes it is a lot of work, running down the parts, pulling the wires making all the connections and more.

Okay, when can you come over?

Thanks for pic. I'm reading about the lithium batteries and link posted. Just want to lose some weight. The big Interstate I have must be 25lbs (or more?)

Larry, AGM is completely different than lithium ion. AGM is still a lead acid battery, and is heavy and big. LI is a whole different animal. Very small and light. It will operate off of the cars alternator. But for charging outside the car, it needs it's own dedicated charger. And if you run it down below a certain voltage, it shuts off and needs the special charger to wake it up. That's because the battery has a microprocessor or something in side to protect the cells.
I used this thing in my drag week car, and it worked out fine, and saved 50 pounds.

Joel, how does it hold up in between rounds running a electric water pump and fan ?

You are safe for 10 minutes of fan and water pump, more than that is a risk. I forgot the water pump on once in the staging lanes during Drag Week. There was a long down time, maybe 1/2 hour or 45 minutes and I went wandering around. When I got back it wouldn't start. It did not get so low that it locked up the battery. A jumper pack started the car to make the pass. I had the special charger in the pit area, along with a jumper pack that has a 110 volt inverter, so I used that to give the battery a good charge.

Thank you! Very intrigued by these lithium batteries now, and reading more on them, and really leaning toward one of these now that you have me looking at them! I read about requirement for unique charger. This sounds like a great option over the moving standard battery to trunk. Thanks! Larry

Pulled the trigger on a lithium battery. All your fault Hemi-Joel

My Diplomat is Group-34, so is this Braille, ultra powerful (and expensive), but I got it at a big discount, and with a charger thrown in (go to their website and "chat" and work a deal if you're interested in buying one). It's 11 pounds so I'm going to be losing probably at least 35 pounds from the huge Interstate I have now and that's going south on me. I'll be able to keep my factory Thermoguard for looks

https://braillebattery.com/products/i34x

Thanks for help all.

Larry

you achieve none of the above. You can go get a modern battery that weighs nothing. There are better ways to archive handling and traction. The only reason I moved my battery to the trunk is because I needed space for the Paxton. In my last build, 70 Charger that ran 11.20's the battery was it the stock location. Do as you please it isn't worth the effort.

I didn't lose 35 pounds? I didn't get a battery that will last much longer than standard battery? I dropped the idea of moving it to trunk after reading a lot of the feedback. I've done many other things for traction and handling (frame ties, solid K frame isolators, urethane bushings, new sure-grip unit, larger than stock tire size, as well as other things). This is probably the last thing; losing a few pounds up front. My last post just before yours says I'm not moving it to rear, and I bought modern battery.