Move Convertible Battery to the Trunk

[WhyNot]

I have a vert and the battery is/was in the front.
The " > " is like a step.
>I removed the 50lb weigh from the trunk.
>Got all the pieces from a donor coupe.
Battery cable, mounting post in engine compartment, trunk battery tray-cover-fenderwell shield.
It is alot of labor but not really hard.
>Drill a hole in the fenderwell drain plug for the battery vent hose.
>The battery tray needs to have the back feet cutdown so it fits flat. Added a couple of screws to secure it.
>I drilled a hole in the inside lip of the battery surround lip for the ground. Clean the paint and nut and bolt then the cable and another nut.
>Mark and cut the side carpet so the battery cover tucks underneath.
>I added a second nut and bolt to secure the bottom back of the battery tray and used a plastic nut for the top securing point.
>Notch the battery cover for the trunk lid shock to clear.
>Mark the first metal wall into the cabin and use a drill with a small bit and drill lots of holes [poor mans nibbler]. File the edges.
>Cut/split vacuum line down the middle. Add silicone inside the line the wrap the newly cut opening. Do the same thing for the bulkhead behind the back set.
>Remove the back seat, front pass seat, back side panel, rocker panel moulding, front speaker cover, glove box.
>Pull the carpet away from the rocker panel. Remove the wires from the channel in the clips, thats where the battery cable goes.
>Where the back seat stills on the metal panel area use a large socket laided lengthwise to bang a largere radius for the battery cable to run.
>From the engine compartment, underneath the ac lines, on the triangle shape part is a metal plug to knock out for the battery cable grommet.
>Remove the passengers side black plastic cowl [like where the wipers are]cover then mount the battery cable mounting post and hold the nuts tight in the cowl, put the cover back on.
>Run the wires up thru the hole and add the grommet.
attach the battery cables onto the post assemble.
>I relocated the negative down lower on the body to clear out the clutter around the old battery box area.
A couple tips " * "
*Take pics of how everthing comes off donor car.
*Wash all the battery parts before you work on them cause the old battery acid dust isnt cool.
*Dont secure the battery cable in the middle until both ends are connected.
*Leave the negative cable off the entire time but you will need to attach the positive to ensure proper fit.
*Dont rush. It will take allot of time.
*Dont tackle this unless you really want to make the change.
I did it to 1-make the battery last longer by keeping it away from the engine heat, 2-provide easy power for my stereo amp installation, 3-be cool like coupe and sedan owners.
Now that I done it, if i would have known what was involved i might have just ran a power line to the trunk for the amps.
It cost me abou $50 for the pic a part stuff, nuts/bolts, etc.
I used a couple 1/2" emt holer clamps to help hold the cable in a critical places.
Now I'm cool.

[WhyNot]

heres some pics as attachments
im kinda dumb and havent figured out to just show the pic directly

[WhyNot]

more pics

[dnguyen1963]

Why do you go through all this work? The gain is minimal for the battery to be in the trunk for a vert, if any. I think BMW already had the weight distribution optimized for the vert.

[hotrodlincoln]

Good job. Nice write up. I did mine only to clean up the bay.

Before


After

[WhyNot]

Why do you go through all this work?

i did because doing projects like this give me the illusion that i have control of my life. thinking about it means that i'm not thinking about the real issues of life, which tend to depress. and the positive feelings of accomplishments keeps the wheel turning. its okay to deceive your self as long as your okay with.

The gain is minimal for the battery to be in the trunk for a vert

well i removed a 50 lb dead weight from the trunk and replaced it with a 30 lb battery so i think thats ok. i removed 30 lbs of load from basically the passenger side front end, maybe i'm kidding myself, but i swear i can feel the difference. the battery might last longer since it cooler in the trunk. since i knew i was adding some amps for my new sound system, i would have to run some wiring anyhow. plus chicks really dig the mods.

I think BMW already had the weight distribution optimized for the vert.

i think they did throw 50lb in the trunk to keep the weight distribution ratios. and even if the original design was optimal, i dont think my cheap kumho tires will ever let me realize the difference.

[WhyNot]

Good job. Nice write up. I did mine only to clean up the bay.

Before
[ATTACH]66124[/ATTACH]

After
[ATTACH]66125[/ATTACH]

sweet ride.
love to have air suspension

[funcrew]

Why do you go through all this work? The gain is minimal for the battery to be in the trunk for a vert, if any. I think BMW already had the weight distribution optimized for the vert.

He did it and posted this DIY so asshats like yourself could point out that the physics of front/rear weight distribution and its effect on handling dynamics become instantly null and void when the car lacks a fixed sheetmetal roof. Kudos to you, dnguyen1963, for giving back to the R3V community by pointing this out. My hat's off to you.

[spike68]

Why do you go through all this work? The gain is minimal for the battery to be in the trunk for a vert, if any. I think BMW already had the weight distribution optimized for the vert.

+30 HP and moar mad skidz bro. Derp.

In all seriousness, why not? It looks much cleaner. To some people that a big gain. Nuff said.

[jeffnhiscars]

How many of us do shit just because and I especially appreciate the advice about the crystal meth. I mean how many of us have made THAT noob blunder !!

Nice write up. Thanks for sharing.

[robrez]

This thread was really helpful but I didn't want to drill any holes, so this is how I did it
First familiarize yourself with the front and rear attachment points for the battery cable and make sure you have all the parts you need. These two pics nail it down.





Then, start from the back, there's a small hole at the bottom right corner of the first bulk head. Then fish it down through the body side panel and pull it through where pictured below.



But even if you do it this way, the cable will be too short to get to the stock distribution block mounting location at the front of the car. Most people add 6" - 12" of cable to the front or rear end of the cable. But then you lose the stock attachments. And especially if you add it to the back, the splice is in a location that's constantly being jostled. My advice is to basically cut the stock cable in half so that the splice is somewhere under the front door sill, where the cable is secure, and the splice is hidden.

Lastly, I used a longer oem negative cable from an older 7 series and attached to the stud on the back body panel. You can kinda make it out at the bottom of the pic above.

One more bit of advice, if you use the plastic battery tray from a coupe/sedan, the battery will tilt toward the front of the car. I'm in the process of modifying the metal tray that the vibration dampener was attached to. It's sits nice and flush and is secured to the car by four bolts. You just gotta figure out how you want to secure the battery to the tray. I'm going to use oem hold-downs, but it's gonna take some welding.



And then when you're done with all that, you can put an iX washer bottle where the battery was and show off your valve cover and headers ;)

[Klug]

Note for future vert guys moving the battery to the rear. Since the stock 325i cable is a few inches too short- make sure that when you do add another few inches to the cable- to buy a 2/0 butt splice (crimp connector) since 1/0 is too small (the cable itself is somewhere between 1/0 and 2/0 but not an exact standard gauge)

I'm using the stock 325i cable from the front, put the 2/0 splice near the door frame and continued back with a e36 m3 cable I had from a partout to the trunk (they turned out to be the same measurements, both length and inner/outer diameter)