Car Not Accepting New Battery

[MotherOfDragons]

Hey all,


I recently had to replace my E46 M3's battery and I'm having some issues I'm hoping I could get some advice on. It all started when I couldn't start my car a few weeks ago -- the battery was probably 7 years old so it was time. It was a BMW battery, and I replaced it with a Duralast Gold Battery H7-DLG Group Size 94R 800 CCA, one that I found recommended by others on these forums. When I first replaced it, I could start my car and everything was great. But just a few days later I could no longer start my car -- it would turn on electronics but when I tried to turn on the ignition, all electronics would die.


I thought the battery was bad so I took it back to autozone and they checked it -- they said it still had 100% charge and that the issue was that I needed to register the battery with my ECU. This is strange because every guide that I read about replacing the battery for E46 M3's didn't say you had to, in fact iirc one explicitly said that you only have to starting with E90s. [1][2][3][4]. Indeed, I have a BMW OBD diagnostic tool but there isn't even an option for battery management for the E46s on the tool, only the E90 and above.


Is there something I'm missing? What steps do you recommend I take to figure out why my car is still failing to start? At this point I'm thinking I might just take it to my mechanic but maybe there is just something stupid or obvious I'm missing that you guys could let me know so that's why I'm asking here first.


Thanks!

[XnWarden]

As you said battery management only started on e90s. My friend had an auto zone do the battery on his e90 anyways and the car would still start. None of the lights or gauges would work, and he had to have it resynced. But it still started.

In your case you have another issue going on. Since it started temporarily for a few days and then stopped, I recommend having it properly diagnosed.

Sent from my SM-G975U using Tapatalk

[All2kool]

As stated, an E46 never requires 'battery registration'.

IMHO, it sound like a bad Alternator or a bad ground. What voltage are you getting while the car is running? There is an OBD sequence that will provide this information.

[dworthy]

+1

Clean the posts and the battery clamps on both sides, then give that a go.

[Muzz258]

When reading your description the first time, I was thinking that is was a stuffed alternator not charging the battery. But Autozone tested the battery and it was 100 % charged, so it can't be that.

Do you have a multi-meter? If so, set it up on DC Volts connected to the jump start terminals under the bonnet/hood and place the meter on the windshield so you can read it from inside the car. It should read somewhere around 12.5 Volts for a fully charged battery. Go to start the car and watch the multi-meter. If the volts drop well below 12 Volts, then the battery is delivering lots or current into something. Most likely a stuffed starter motor. The other possibility is a stuffed cell in the battery, which can be found through a load test at Autozone.

[MotherOfDragons]

Thanks for the suggestions everyone. I checked the engine bay terminal connections and they were tight. I then decided to reinstall the battery, but first I cleaned the terminal connectors that connect to the battery (thanks @dworthy) with some distilled vinegar and lots of scrubbing to remove some minor deposits that had built up on the positive one especially. I then reinstalled the battery making sure the connections where extra tight, and voila! That seemed to do it. Seems like it was just a case of a slightly imperfect connection. Glad it seems to be working now but if my car doesn't start again tomorrow... I'll let you know. ����