Most European cars that relocate the battery to a different location is purely for weight distribution. I know the 750i and 850i's had dual battery set ups with one on each side in the rear of the car. the 5 series has run a battery under the rear seat for a good while. The 3 series seemed to be the one they kept the battery under the hood for most of its existence. The 7 series ran dual batteries because of all the electronics in the thing. They shipped with 160 Amp alternators and dual batteries to keep up with the load. The system was set up start the car with the battery with the higher charge in it. the isolator would keep the things charged properly. If you have ever looked under the hood at the V12 and all the space the damn thing took up there is a clear understanding for batteries in the trunk.
When ever we set up a car for track use, it was a 3 series body so first step was to get the battery to the rear over the rear axel.
My E46 coupe had the batter in the back as did the bride's E91. The older ones were up front?
< '81 CJ7, Chev power. Leaf springs baby!
2016 JKU Sport
The good guys: Synergy, Artec, MetalCloak, MCE
- 2.5" MC coils, Synergy arms and drag link flip.
- 37" BFG MTs on 17x8.5 -6
2013 GC... 5.7(MILF command centre)