Moving Battery to Trunk..Vert.

[BMVUU]

I need to move my battery to the trunk on my 325ic. where should I cut? I have all the parts from a 318is I parted and Its been a while, so I need some visual aides. Is there a step by step site on how to do this?

[Dustn525]

You don't need to cut or drill anything, besides the liner in the trunk. Here's a pic with the weight removed and the bottom of the left side trunk liner cut off:


That's $25 in change that I found under there. Run your ground cable like it is in the picture, hard top cars have a grounding point closer to the back of the car, but verts (or at least mine) don't have it. Sand some of the paint off of the grounding point to get a good connection.

There's a metal tray that's fastened on top of the weight. Take the tray off the weight, it serves as the battery tray. Here's a pic of it, I had it out to give it a rust-proof coating. Notice the holes line up with the 4 bolt holes in the trunk.


You don't want the weight anymore, your battery basically replaces it. When you run the battery cable through the rear of the car it gets a little tricky since you don't want it to interfere with the power window mechanism. The cable goes through the firewall on the passenger side where the AC lines go through. I used a distribution block from a car stereo store temporarily until I found an OE one. The illustrations on RealOEM.com should help you too.

One thing that people don't take the time to do is make or buy a hold-down. Although I like to stay OE as possible (as close to the e30 M3 cabrio, battery-wise), I run an Optima battery which is sized a bit different than the OE battery. I set the Optima on top of the tray, marked drilling points, drilled the 4 holes which line up with the ones on the bottom of the battery, then applied touch up paint to the exposed bare metal, and another spray job of the roast proof coating. I could have fastened the battery using bolts/nuts which would have been more pleasing to the eye. In this install I used zip ties (!), the strength of the 4 ties combined is enough the hold the battery securely even upside down (not recommended). The ties also won't rust in a potentially corrosive application.

Note how I aligned the battery, so that the battery and tray can be removed as one assembly, by the 4 tray bolts. Of course, if you use a conventional hold-down, this won't be a problem. Personally I hate the ones that use wing nuts on top.



Hope someone finds this useful, will post a full write up soon.

I am not liable for anything!.

[smonkbmw]

how does a vert handle after moving that weight to the trunk? i mean isnt it heavier in the rear because of the top and what not? id think youd want to balance it out by leaving the battery in the front?

[BMVUU]

any pics of where it goes through the firewall?

[Dustn525]

how does a vert handle after moving that weight to the trunk? i mean isnt it heavier in the rear because of the top and what not? id think youd want to balance it out by leaving the battery in the front?

Well, when you move the battery to the trunk, you also remove the ballast that is in the same place. So, you're taking about 50lbs off of the total weight, and moving another 40-50lbs or so from the front to the back. It handles just the same. The e30 M3 (europe only) Cabrio came with the battery in the trunk like so.

any pics of where it goes through the firewall?

I'd have to remove my glovebox to snap a good pic, remove your glovebox and you'll see what I'm talking about. Good luck.

[douglasm5]

Dustn525 - Thanks! I've been wanting to do this!

I installed an s50 in my '93ic and you can really feel the extra weight in the front. The battery sits pretty high in the front and I'm hoping that getting to the back, and lowering it, maybe the car won't push so easily.

If you get a chance to post more pictures, I'd appreciate it very much!

[joeuser528e]

I just did mine. I took the cable off a junkyard 325e I think, plus a battery tray, tie down, distribution box and a few other misc things. I did not run my cable through the inner fender, I ran it along the interior and under the rear seat, like they do it from the factory. Some people have a big enough hold at the corner of the rear-seat back and the fender, but mine was too small so I had to drill it out a little bit on each side to make it a straight shot.

To run it from the engine bay you need to pop out a little metal piece right near the battery. See the writeup

There are two holes already drilled for the distribution box (found right behind where the front battery goes). My battery cable was not long enough (by maybe two inches) once it got all locked down under the carpet, so I had to re-mount the distribution box a little bit towards the passenger fender (used one old hold a drilled another one two inches to the left), and the battery cable fit.

I used the grounding cable I got from the 325e, and my grounding point was one of the bolts that hold on the bumper. I just sanded down the area around it to the bare metal. There's a couple of different misc bolts around that area that even the short factory grounding cable will reach, so just choose one.


I haven't really gotten a chance to drive it yet, but my car has a problem with understeer, so the rear battery should help. Whenever people ask me what I did this weekend, and I tell them "rear battery conversion", "why?", "weight distribution reasons." They always look at me funny. I just couldn't live with my car having that much weight in the front.

Here's the writeup I refered to:
http://www.r3vlimited.com/board/show...hlight=battery

[Dustn525]

For those who wanted to see a better 'vert rear battery write up, sorry for being lazy...figured I'd give this thread a bump and I added another pic up top. I'm installing an alarm this week, so I'll have some of the interior trim panels out, and I'll take more pics and do an all new, complete write up on on the battery. I'll do one for the alarm too, but it may take awhile since the weather here sucks BALLjoints.