battery spec for a 91 318is?

[tiloulou330i]

Does anybody know the battery spec for a 1991 e30 318is?And where can I find it?Thanks in advance!!!!
Filbert

[RomeoMike]

Buy an Optima Redtop group 34 (around $125 at Sam's Club). Fits nicely, no acid to vent or crap all over your battery box, reliable as can be.

The extra red fused wire you see on the positive terminal goes to a keyless remote unit (another fun mod).

[djb2]

Optima batteries are 2X to 3X the price of a standard battery, and might not last any longer. They do handle deep discharges better, but you don't need most of the benefit of valve-regulated venting (operating in any orientation, less likely to vent corrosive mist).

Standard battery: 47-3
Approximate dimensions 6.5"x6.5"x9.5"
Stock group 48, group 49 (1987 635csi) will also fit
Alternate for e30
Interstate MT-48 550cca 75months
35.60 pounds
11.38"x6.88"x6.88"

Interstate MTP-H6 640cca 85months
46.10 pounds, post, positive right
LWH 10.94"x6.89"x7.48"

MTP-93, 850cca
48 pounds
LWH 14.38"x6.88"x7.688"


I don't know specifically about the engine compartment tray, but the trunk mount has mounting holes for three different length batteries. The battery listed for the
car is group 47, but group 48 and 49 will fit as well.

Here is a really useful guide for the sizes:
http://www.rtpnet.org/~teaa/bcigroup.html

The larger batteries usually have higher capacity with thicker plates.
With similar construction a larger, higher capacity battery will last
longer than a smaller battery. The only down-side is that they weigh a
little more.

Here is the curious thing about the market: To keep things simple,
different batteries are often priced the same. The application books guide
customers to the least-expensive-to-make battery that will work. But
the best deal is usually getting the largest battery that will fit.

A battery warranty suggests how long the battery is expected to last
but, much like tires, there is a strong element of marketing. There is
a good chance you won't have the documentation (or memory) to take
advantage of the warranty. Even if you do have the paperwork, the
warranty is pro-rated. A battery that dies a year early yields only a
few dollars discount off of a new one, while locking you into the same
brand which is likely not on sale. So the brand has a motivation to
over-state the life of the battery.