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Battery (trunk) relocation - parts compatibility?


Pablo M

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I've done a bunch of research on relocating the battery to the trunk on here. 

 

Yes, I've read about under seat being better. 

Yes, I've read about shock tower brace generally understood to be ineffective.

No need to rehash those topics.  :)

 

I got a TEP rear brace/battery holder as part of a lot of parts I bought, so effectively free lol. 

I recently had to remove the battery to replace the oil filter. 

I like the idea of moving some weight rearward. 

 

I know the easiest (I've found) was to use the e30 battery cables and engine bay junction box (connector?).

 

My question: Are there other known cars that you could also use the battery cables and such for this relocation? Does the same/similar era 5 series (e12/e28) also use same cables and junction box? Are there newer cars, like 20 year old cars (that I might more easily find in a junk yard lol) that would work? 

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2003 e39 M5 (daily)

1986 e30 325es (sons car)

1972 2002tii (fun daily alternative)

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Hello Pablo,

 

FWIW... I have a 2008 Audi TT, and the battery is located in the trunk. There are two charge points located at the  driver's side shock tower as shown in the pictures below. For your reference the part number of the cable is 8J0071227A, 8J0971227D and the cable runs back to the rear where it hooks up to the battery and also has a lead that I'm sure runs to the alternator for charging.  I hope this information is helpful. The negative connection is just a metal stud that looks to be screwed into the body of the car.  The cable is black in color, however the plastic connector is red to note that it is the positive post, and it looks like the cable holder thingy could be easily adapted to our cars, the only issue would be the length of the cable. The TT battery is located at the tail end of the trunk of the car which would make the cable sort of longer, and if the 2002 battery is right between the rear shock towers, this might be a solution, and there are some of these cables on eBay, etc. the only concern would be the length, of course longer being better then short... no jokes here... LOL

 

 

 

762144062_positiveterminal1.jpg.86155c23d334bd7e7de322d6e85e3997.jpg

 

 

109875763_positiveterminal2.jpg.eb0da5059dce772577e58c7ac74da9c5.jpg

Edited by larry_in_socal
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I don’t think it matters what car you get the cables from. If the battery is in the boot (trunk 😉) then the cables will be up to the job I’d have thought. Don’t forget the smaller positive cable to run alongside that I recently learned about.

Phil

1975 1602 with an M42 engine.

Project thread http://www.02forum.co.uk/viewtopic.php?f=11&t=14853#p107713

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I went to an Interstate battery store and asked the guy if he would sell me some battery cable. I think I bought 11 feet. He cut it off a spool and crimped the proper connections to the ends for me. I think it was $3 a foot. 

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1974 2002 Tii-SOLD

1978 911SC Coupe

1988 Landcruiser

2020 M2 CS

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7 hours ago, PhilC said:

I don’t think it matters what car you get the cables from. If the battery is in the boot (trunk 😉) then the cables will be up to the job I’d have thought. Don’t forget the smaller positive cable to run alongside that I recently learned about.

What smaller positive cable? You mean the really thin secondary wire? Or from the firewall junction box termination to starter?
 

And cables from more modern cars have some kind of fusible link at the battery end that is tied to the airbag system, effectively killing the power system except the accessories if there a crash. 

Edited by Pablo M

2003 e39 M5 (daily)

1986 e30 325es (sons car)

1972 2002tii (fun daily alternative)

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1 hour ago, Pablo M said:

What smaller positive cable? You mean the really thin secondary wire?

Not the short power cable to the starter.

It's the smaller size wire that runs from the battery plus terminal to the firewall terminal block on E30s.  It's a dedicated soruce of 12v to the DME (ECU).  It also has a fusable link located about a foot from the battery.  If it blows, a circuit breaker from NAPA can be wired in it's place.

A radiator shop is a good place to take a leak.

 

I have no idea what I'm doing but I know I'm really good at it.

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Yes, E36 cables work well, too, from the 6 cylinder cars.  If I remember, the E36

has a somewhat lighter wire, which is good.  The BMW way is very... well,

low voltage drop at the cost of a LOT of weight.

 

The E46 cables are also very good- however, those have the explosive charge

buried in the positive terminal.  And are truly huge, probably 3x as heavy

as is really needed to start an M10 (or an M54, or a SCummins) reliably.

 

If your 2002 has an EFI system, the second wire for power's probably not a bad idea.

However, a carbed, points (or hotsprk, prtrnx, etc) car isn't going to care that the

voltage from the battery's an extra half- volt lower at the points, and a bit noisy.  It'll start.

Most of the voltage drop in starting's in the lead

(that's Pb, lead the metal, not the wire lead.  stupid Engwich)

in the battery, and the second wire's just trying

to get the most it can as cleanly as possible out of the positive terminal.

 

The car I race (occasionally)  has a 2awg wire from the battery through the disconnect,

and none of the rather basic computers I use seem to care that that's the only 

connection to the dinky little battery in the back seat.

 

fwiw,

t

 

 

"I learn best through painful, expensive experience, so I feel like I've gotten my money's worth." MattL

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I found my junction box on a late 90s 5 something, the cable was not a good fit for an 02.

It had a heavy cable teed off .

Pretty sure E12 and E28 batteries are located in left side engine bay.

Not really sure what the big hoo ha ha is about the E30 cables, they are actually kind of short and limit you in where you can locate your junction box. Plus trying to locate one can be a challenge.

Just make one, that way you can locate your junction box where you wish and cut to fit.

I used extreme battery cable (has an extra layer of sheathing)

Solder the terminal lugs dont crimp (unless you have access to an actual, expensive crimper that crimps, not squishes)

Cable, solder plugs, HD heat shrink can be found here.

Note the green/yellow wires I ran with the cable.. a 10 ga and a 12 ga for possible use later. probably should have routed a couple more when I was in there.

 

IMG_3333 2.JPG

IMG_3334 2.JPG

IMG_3336 2.JPG

IMG_3337 2.JPG

Edited by tech71
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76 2002 Survivor

71 2002 Franzi

85 318i  Doris

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Thanks for the info everyone. Got lucky on my trip to the junkyard this morning and the e30 that was there for two weeks was surprisingly not picked over. Got the battery cable from trunk to firewall, junction box, and cable to starter. Cheap too. Also got a good negative battery cable from an e36 just in case. I'll remember to maintain a ground from engine to chassis too per the link above. 

I'm not in a hurry to do the project (I have other priorities for this 2002) but good to know I have what I need for when I'm ready. 

 

By the way, e28 battery is under the seat. Didn't matter though as that car wasn't there (it was listed to be). 

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2003 e39 M5 (daily)

1986 e30 325es (sons car)

1972 2002tii (fun daily alternative)

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