My '94 325is is on its original battery (it has only 35,000 miles). I had it sitting for 2 weeks in the garage and now it's completely dead.

Since it's 7 1/2 years old but low miles, do I necessarily need a new battery? If so, then what should I replace it with? Note that I'm running a 150x2 rms amp and sub in the trunk.

Thanks for your help!!!

Did you disconnect the battery before you let it sit? If you have a charger try charging it and check the electrolyte level and the specific garvity with a Hydrometer and that sould tell you how the battery is doing.
Hope this helps you

since your battery is 7 1/2 yesrs long, I guess it's time for a new battery. many E36 M3 battery lasts only 2-4 years from what I know. you can replace with another stock battery or aftermarket such as interstate or the optima red top, which has better CCA than the oem battery. for our car, it's group 2, i think. in my opinion, since you are running some amps, buy the optima but you'll need some kind of bracket to fit it in the trunk. go to the audio board and look for Jay(aka Luni2z) and ask him about it. he is an audio expert and he knows stuffs.

Hi Shawn. No, I didn't disconnect the battery. I'm going to get it jumped-started in about an hour (hopefully it'll take) and wanted advice on whether I should get it replaced immediately. I guess I'll drive it to a shop and have them test the battery.

Any recommendations on a new battery (size, power level, etc.) if I need it?

if the battery holds the charge fine dont replace it just let it be

autozone/most any autoparts store will check the battery for you to see if it still holds its charge free

On an older, completely dead battery, do NOT let them use the rapid charge method. Get the car jumped and drive it for about 10 minutes. Be aware that idling the car will NOT charge the battery effectively. Go drive it. Take tools with you to remove the battery at Autozone and take it in for the more sophisticated out of circuit test. If it tests ok, good. Put it back in and go. But even if it tests good, do NOT let them perform a rapid charge on it. Either recharge it by driving it or putting it on a trickle charger for several hours at about 2 amps.

Jim

For piece of mind I'd replace it anyway. There are some Interstate batteries that are smaller (less weight) with higher CCA's, but I don't have the model numbers on me right now. The only thing is that they don't fit the brackets in the trunk.

Thanks for all the replies! Well, I got a jump (and learned about the very cool "positive jump nut" in the engine compartment (I used to drive a Miata - also with the battery in the trunk - and you'd have to jump it from the trunk - big pain)), and it started right up and I drove for about an hour. Then, I let it sit for a bit and it started right up again So it seems OK; however, with winter coming and the fact that it drained on only 2 weeks of sitting, I'll probably get a new one next weekend at autozone (or at least have them test it).

Thanks again, all. :boing:

if you will be letting it sit for periods of time disconnect the battery and/or purchase a quick disconnect switch for the battery

or buy a trickle charger and let it stay on there for as long as its being stored

why dont you try buying and Optima yellow top deep cycle battery. I like it, it has a 3 month shelf life and its a dry cell, especially if you have a stereo system it has 120mins reserve capacity and can be rechared over night using the charger, i havent had problems with it.

my system consists of 2 eclipse 12's with and dianmond hex 500s components and eclipse 6x9's with the eclipse 7002 lcd and 2 crossfire tek amps 50 x 4 and 150 x 2

I would change it; its a pain with a dead battery, and the winter puts quite a toll on it; 7.5 years is a long time for a car battery, in my opinion, and BMW's definetly are very electrically dependent vehicles.