Battery relocation

JacobM03

1st Gear Poster
Joined
Dec 26, 2023
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55
Location
Ontario
Vehicle Details
1992 Thunderbird Sport 5.0
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Anyone do a battery relocation to the trunk?

If you did could you show pictures and what it requires in terms of battery cable and length.

Also where would the battery cables be routed from the trunk?

Thanks in advance
 
I'm working on one now. I'm going to use the stock battery box/support/holddown, with a bolted down holddown across the top I don't want a battery flying in an accident. I'm using 4 awg wire, that I just happen to have. If it's too small, I'll buy bigger. Matt has pix if his, iirc, in his build thread. He mentioned the Lincoln LS cars being a good source for battery wires to the back. There are two wiring trays under the carpet, one on each side. I usually run audio down one side, power down the other. Matt also pointed the starter and motormount is on the pass side, about 2" on the other side of the floorboard. :) Amazon sells cable glands for big wire, so you won't get a wet floorboard. Starter has the Big + wire to the stock battery, andthe motormount is the ground connection to the stock battery.
 
Here’s a few pics of my setup @Grog6 mentioned.

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This isn’t the finished version obviously but the routing is the same, I don’t feel like laying on the floor today to take pics lol

As mentioned this is using a two Lincoln LS cables, I think the junkyard charged like $10ea and that is a killer deal for 0 gauge cable and since it’s routed through the interior in those too it’s usually in excellent shape free of corrosion.

DSC03304.jpeg

I used the whole cable to run from battery to the firewall, from the firewall I bolt it to another cable with a mega fuse where I then run it through that grommet down into the inner fender under the frame rail to the starter. Then another cable from the starter to the fuse box(these two cables I made from 1 other LS cable I cut in two). Ground I simply ran from the battery to a factory ground point in the inner trunk structure.
 
Beautiful install. ) awg is considerably bigger than what I was going to use. 0 awg is about 6 bux a foot no 8 bux now on zon. I don't have the cash for that, but I do have bigger wire, I guess I'll use it, lol. I guess there's no weight penalty for adding all the bracing to it, if I'm using 200 lbs of copper, lol. I need to order some terminations for 350 mcm cable, lol. No, I'll go with the 4awg. It's rated at 120A, so technically if it shorts somewhere, and the fuses don't open, the alternator or battery could set the passenger compartment on fire. I guess I can take that risk. ) The car stereo draws 56 A when jammin, so That's about what it will see maximum. I'm hoping the capacitor doesn't cause problems. I had interesting effects from the filter I built in the subaru. I used rg8 to move the power to the back, a huge inductor, and 2x 190,000uF The starter ate brushes, and there were other odd effects. For one thing, 81 subarus aren't known to roll start, as they have a computer. You don't normally get power without a battery. But, the combo of stereo gear, and those caps let it build voltage, even with a totally dead battery, which came in handy over the years. Park on a hill at the lake, and the car will start, even after the amps and deck shut down. :rofl:
 
If you intend to be NHRA legal, you'll need to follow the rules for the battery disconnect and sealing it off from the passenger compartment.

I used 2/0 cable.

I used to run an Optima in an open arrangement, hence the rear firewall.

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After switching to a typical battery, I installed the Moroso box. Note the battery disconnect on the right.

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You can see the firewall here:
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When I ran the car at the track, I'd swap out the taillight for one with a hole through it, and install a bell crank and rod onto the battery disconnect to be NHRA legal.

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That's the way I'm envisioning doing mine. I did buy an 8mm battery holddown to go across the top. I have a 1/4 " steel plate for under the trunk, to set Nutserts into. Depending on how well they hold, I may just drill and tap the piece I have.
 
IIRC the battery hold down is supposed to be attached through the frame rail in (2) places, 3/8" bolts. I am using 2/0 welding cable with a marine style bulkhead at the firewall. Mega fuse close to battery. Made my own battery mount. I don't have a firewall or cutoff switch yet, but my battery is vented to atmosphere.

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If that moves around the battery is likely the least of your problems.
 
I don’t remember seeing a rule about it attaching to frame rail, the biggest thing I remember about mounting was not using crappy hardware like J hooks. I’ve seen legal cars at the track with the battery mounted it in their spare tire wells so I don’t know how they’d get by if that’s the case
 
8.1 BATTERIES

All batteries must be securely mounted and may not be relocated into the driver or passenger compartments. Rear firewall of .024-inch (.6 mm) steel or .032-inch (.8 mm) aluminum (including package tray) required when battery is re-located in trunk. In lieu of rear firewall, battery may be located in a sealed .024-inch (.6 mm) or .032-inch (.8 mm) aluminum, or FIA accepted poly box. If sealed box is used in lieu of rear firewall, box may not be used to secure battery, and must be vented outside of body. Strapping tape prohibited. A maximum of two automobile batteries, or 150 pounds (68 kg) combined maximum weight (unless otherwise specified in Class Requirements) is permitted. Metal battery hold-down straps mandatory. Hold-down bolts must be minimum 3/8-inch (9.53 mm) if battery is relocated from stock and other than stock hold-downs are used ("J" hooks prohibited or must have open end welded shut.).


8.4 MASTER CUTOFF

Mandatory when battery is relocated, or as outlined in Class Requirements. An electrical power cutoff switch (one only) must be installed on the rearmost part of each vehicle and be easily accessible from outside the car body. This cutoff switch must be connected to the positive side of the electrical system and must stop all electrical functions including magneto ignition. The external control switch for this cutoff switch will be clearly indicated by a red flash inside a white-edged blue triangle with a base of at least 12 cm (see drawing 25). The positions must be clearly indicated with the word "OFF". If switch is "push/pull" type, push must be the action for shutting off the electrical system, pull to turn it on. Any rods or cables used to activate the switch must be minimum 1/8-inch (3.2 mm) diameter. Plastic or keyed switches prohibited. Switches and/or controls must be located behind rear wheels on rear engine dragsters.
 
If that moves around the battery is likely the least of your problems.
If you are referring to me, that thing is solid as a rock. Goes all the way through the frame rail with (2) 3/8" bolts. Nuts are welded to bottom of frame rail so they don't vibrate and fall off. The top nuts are serrated and flanged as well never had an issue with loosening.
 
Here’s a few pics of my setup @Grog6 mentioned.

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This isn’t the finished version obviously but the routing is the same, I don’t feel like laying on the floor today to take pics lol

As mentioned this is using a two Lincoln LS cables, I think the junkyard charged like $10ea and that is a killer deal for 0 gauge cable and since it’s routed through the interior in those too it’s usually in excellent shape free of corrosion.

View attachment 5490

I used the whole cable to run from battery to the firewall, from the firewall I bolt it to another cable with a mega fuse where I then run it through that grommet down into the inner fender under the frame rail to the starter. Then another cable from the starter to the fuse box(these two cables I made from 1 other LS cable I cut in two). Ground I simply ran from the battery to a factory ground point in the inner trunk structure.
Could I see where you mounted ground?

Also why did you run the cable to the inside of the wheel well instead of inside the engine bay down to the starter?

Where did you route the cable from starter to fuse box too? Like where did you attatch it specifically?

Finally, is there a location I could just put a cable gland to avoid going through the grommet and in the fenderwell?

Thanks!
 
I don't understand why people relocate their battery. just seems pointless unless you are adding a 2nd battery for a stereo set up. what is the "upgrade" by doing this? I added a 2nd battery on my SC but thats because I have a pretty elaborate stereo and needed it. but i'd rather have trunk space for whatever it is thats needed to be placed in the trunk vs loosing space by just moving a battery there. don't get me wrong I'm not knocking it, I'm trying to understand why.
 
I don't understand why people relocate their battery. just seems pointless unless you are adding a 2nd battery for a stereo set up. what is the "upgrade" by doing this? I added a 2nd battery on my SC but thats because I have a pretty elaborate stereo and needed it. but i'd rather have trunk space for whatever it is thats needed to be placed in the trunk vs loosing space by just moving a battery there. don't get me wrong I'm not knocking it, I'm trying to understand why.
Better weight distribution. These cars are so front heavy that 60# makes a good bit of difference.
 
I don't understand why people relocate their battery. just seems pointless unless you are adding a 2nd battery for a stereo set up. what is the "upgrade" by doing this? I added a 2nd battery on my SC but thats because I have a pretty elaborate stereo and needed it. but i'd rather have trunk space for whatever it is thats needed to be placed in the trunk vs loosing space by just moving a battery there. don't get me wrong I'm not knocking it, I'm trying to understand why.
To save room in the engine bay/clean up abit and to relocate a bit of weight, I dont use the car to haul anything in the trunk really so it doesn’t bother me.
 
Could I see where you mounted ground?

Also why did you run the cable to the inside of the wheel well instead of inside the engine bay down to the starter?

Where did you route the cable from starter to fuse box too? Like where did you attatch it specifically?

Finally, is there a location I could just put a cable gland to avoid going through the grommet and in the fenderwell?

Thanks!

Green screw is the battery ground
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As for the routing into the wheelwell I didn’t like how close the cable came to the exhaust if I just dropped it down from the hole to the starter, running it through the hole in the apron and under the frame rail gives it a nice safe low heat shot to the starter.

I don't understand why people relocate their battery. just seems pointless unless you are adding a 2nd battery for a stereo set up. what is the "upgrade" by doing this? I added a 2nd battery on my SC but thats because I have a pretty elaborate stereo and needed it. but i'd rather have trunk space for whatever it is thats needed to be placed in the trunk vs loosing space by just moving a battery there. don't get me wrong I'm not knocking it, I'm trying to understand why.


For me the space it takes up is a total wash since my car came with the factory 10-disc CD changer there that I no longer need with a modern stereo. Conveniently the battery relocation took away the need to seek out a new trunk carpet since the tray covers the various holes for the changer mounts/wires.

YMMV but for me it made perfect sense at the time since my stock cables needed freshening too. Relocation made for a creative fun project vs. a boring maintenance task, that’s what motivates all my mods really.

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For me it was weight distribution and room under the hood. My intake tube and filter currently reside where the battery was in the stock location.
 
Weight distribution and space under the hood for me. There's still plenty of room for stuff in the trunk, even with the battery, methanol tank, and subs back there. I've had no trouble carrying enough luggage for week long trips for two people.
 
The only thing that could be an issue is golf clubs, or the like. Otherwise the trunks aren't exactly small. Even with property planning they should fit fine.
 

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