How-to install a battery in the trunk

Tired of cursing at your BMW every time you change the oil filter? Wouldn’t it be nice to have a little extra room in that engine compartment? Would you also like to improve the handling of your BMW by eliminating some of the under-steer? There is one simple solution for your 1600, 2002, or tii: get that battery out of there and put it in the trunk!

All you need is 10 feet of #1 gauge wire, a 1-1/2 foot length of wire with an eyelet at each end, a battery terminal, an eyelet terminal, and a six inch to one foot battery wire to ground your battery in the trunk.

If you have an older BMW it’s easy, use the battery holder in the engine compartment because it just unscrews. Take it out and cut off the excess with a hacksaw; all you need is the flat surface to mount the battery on with the hand clamp. If you have a newer Bimmer it’s a little different because the battery holder is welded in there. It’s up to you what you do with it; if you can use it, do so; if not, get one at your dealer’s or a junkyard.

Route the wire into the passenger compartment by drilling a hole through the firewall ahead of the driver’s side just under the dash. Then lead it over to the passenger’s side under the dash and behind the console, then down along the bottom side of the tunnel, under the passenger seat, and under the rear seat, then fit it through the slot at the bottom of the rear bulkhead into the trunk. Put some rubber grommets in any holes you use. Just a little extra protection for the wire, but it’s not absolutely necessary

You can mount the battery on either side of the trunk. It’s best between the wheel wells as there you can secure the battery holder with some sheet metal screws to the metal underneath using some rubber spacers in between, and you get better weight distribution with the battery closer to the center of mass of the car. This way, also, you have plenty of room left in the trunk. However, it may be a bit hard to check the water level here unless you have a Sears battery they’re a lot lighter and you can see through the case to check the water.

Make the proper wiring connections it’s easy to figure out. Ground the engine to the chassis using the wire with eyelets at both ends. You will have to solder or crimp the eyelet terminal to one end of the 10-foot wire and attach it to the starter. Put the battery terminal at the other end and attach it to the battery.

The weight change is amazing you’ll have to readjust your headlights. If you haven’t
removed the front spring strut spacers, do it.

Since I’ve changed the battery location (about a year ago) I’ve put in BMW heavy duty springs in the rear and thinner rubber spacers (one dots). The car handles great N now neutral with a bit of over-steer when I power through comers N just what I wanted.

Author: Robert L. Kozik


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