4RINGSx3

Need to replace the battery in my '95.5 S6. Current battery is an Interstate MTP-91 (installed in Sept. 2012). Looking at Interstate's website appears that battery no longer exists. They show a MTP-48 for a '96 A6 and MT-41 for a '94 S4. I'm aware of battery height issue as relates to coming in contact with steel "springs" on underside of seat cushion so the MTP-48 at 7.5" high may not be the best fit. AC Delco has a 91A (6.9" high) that may work.
I've checked the battery group sizes per BCI and it indicates the following (L x W x H): Group 91 (11 x 6 7/8 x 6 7/8); Group 48 (12 1/16 x 6 7/8 x 7 9/16); & Group 41 (11 3/16 x 6 7/8 x 6 7/8).

What brand & size are people using these days? In advance, Thanks.

Mallet1218

A bit of delayed reply, but I can tell you I recently bought a battery from Federated Autoparts, and they just gave me whatever their catalogue lists as "proper." The battery I got sits really close to the seat springs, though, but so did the one it replaced. To take some worry out of the equation, I took an old rubber radiator hose, sliced it up the middle, and cut and zip-tied sections to cover each terminal. Crap would really have to hit the fan for those terminals to contact the seat springs with that setup. The car isn't near me, but if you want to know the exact battery model I used, I can look and find out.

tigerwillow1

There are other sources for group 91 batteries, OReilly and NAPA being two of them. Autozone has a "european" spec battery if you look it up with the make/model. With group 41 you lose the vent. Many of us use it anyway. The group 41 battery is a bit longer than the 91 but fits fine in the space. If you have the holdown bracket that engages the bottom of the battery it may not work with group 41. The bracket that holds the top of the battery works with either.

UrS4boy

Just remember that the OE batteries were Group 41 vented. Height and venting (with a tube and hose) are important. Otherwise there is a potential for fire.