So I have a heavily modded E36 with 1000w RMS stereo, 4 HIDs, spal elec radiator fan, electric aftercooler fan, electric water pump, normal elec accessories like V1, radar jammer, etc. And have had a blue top optima (starting/deep cycle) for about 6 mos. If I leave the car sitting with only the alarm on for two days it won't start and has to be jumped off. This has been progressively worse, and there have been occasional rought idle issues which I can't help but wonder if it is from low voltage. Anyway, not sure if my alternator is shot (I get 13+ volts with the car running) and I know it is only the smaller 80A I believe alternator. I had a conv M3 with a big stereo and never killed the battery, but it had the 120A alternator from the factory. I was thinking about putting another optima where the spare tire goes and would like to see pics of how someone else did it, or hear any other input on how to make sure it's not the alternator and I just need more battery power. With an optima the car shouldn't be dead after 48hrs.

Anyway, not sure if my alternator is shot (I get 13+ volts with the car running) and I know it is only the smaller 80A I believe alternator.

13 volts is not enough to charge an AGM type battery such as your Optima. You need over 14 volts, and ideally about 14.5 volts. With 13 volts, it would be difficult to even maintain a conventional lead-acid flooded cell battery.

It's time to invest in a new alternator.

Matthew

I have a 140 amp alternator (rebuilt from bosch, 1.5 years old) on my M3 that will fit yours perfectly

99MPower's car
http://memimage.cardomain.net/member_images/9/web/2145000-2145999/2145887_40.jpg

I agree with all the comments about the alternator. Adding another battery would even strain your electrical system more, rather than improve things.

Hey ca1242,
Got any pics of your subwoofer set up you can post in this thread (http://forums.bimmerforums.com/forum/showthread.php?t=667617)?

Hey ca1242,
Got any pics of your subwoofer set up you can post in this thread (http://forums.bimmerforums.com/forum/showthread.php?t=667617)?

Talk about threadjacking! ...give me a few minutes

I have a 140 amp alternator (rebuilt from bosch, 1.5 years old) on my M3 that will fit yours perfectly

Are you bragging or trying to sell me something?:D How much do you want for it? I went to advance auto today and they hooked it up to their machine and it shows 13.99V at about 2500RPM, and 65A of charging output. They also show that the diode is good in the alternator, however they check that from the trunk, and that the battery is still good just not fully charged. This is after leaving the car on a 1A trickle charger for 36hrs. The car started up better than ever, and that also told me whatever was draining the battery had to be less than 1A or my charger would not have been able to overcome it. Alarm shouldn't kill the battery in 2 days, so I guess my alternator is working, just isn't strong enough for what I use it for and the batery slowly gets weaker as I drive it. Okay, but that STILL doesn't explain why it goes completely dead when the car is parked with nothing running for 2 days.... Oh and it turns out I have the blue top starting battery rather than the combo starting/deep cycle battery.