I guess that everyone's batteries are dying these
days.. I called Interstate and they have 2 batteries
that will fit the M3.. a MTP-91, which is a standard
group 48/91 (smaller than stock) and MB66-60, which I
presume is the same as a group 92, which would be the
same size as stock. I opted for a group 48/91 since I
live in TX and would rather save 10lbs than have an
extra 50 CCAs.
You can also get the exide 48/91 which has 60M
warranty and has the vent on the correct side of the
battery. It's about $10 cheaper than the Interstate.
BTW, my old battery was the original and lasted from
4/94 until this week. Pretty good, eh?
-Matt
Use Interstate's website to find the specific battery they recommend for your model BMW:
http://www.interstatebatteries.com/estore/search.asp?N=21+4294574641&Ntx=&Ntk=&Ntt=&Ns=product+Type%7c0||Rank|1&Nu=Part+Number&js=1
BMWs tend to the following guideline for batteries in the USA
BCI Grp # Interstate Type CCA* CA/ RC Warranty Dimensions (inches)
MCA** (Min.) (Months) L x W x H
E30 4cyl Group 47 [MT-47] 590 740 85 75 9-5/8 x 6-7/8 x 7
All 6cyl Group 48(91) [MT-48] 550 690 96 75 11-3/8 x 6-7/8 x 7-1/5
[MB66-60] 550 690 96 60 11-3/8 x 6-7/8 x 7-1/5
Group 91(48) [MTP-91] 700 875 120 85 11-3/8 x 6-7/8 x 7-1/5
All 8cyl Group 49(93) [MT-49] 750 940 130 75 14-3/8 x 6-7/8 x 7-1/5
[MB88-60] 750 940 130 60 14-3/8 x 6-7/8 x 7-1/5
Group 93(49) [MPT-93] 850 1065 155 85 14-3/8 x 6-7/8 x 7-1/5
MT-42 [example: 1984 BMW 318i(alternate)]
Pro-rata warranty: 75 months