[alexwhittemore]

My 2009 has its original battery. It's got some problems that COULD BE (but likely aren't) ignition related, and it always turns over, but sometimes it labors for a while, especially after I haven't driven it for a week or two. Like, maybe cranks 2-3 times before ignition, where when I first got it, it'd barely turn once.

I brought it to pep boys for a quick load test: it's a 95AH battery, 900CCA. It was measured at 795CCA, but only 12.36V which, by their machine's estimation, is a 55% state of charge. Given that I'd been driving it around for an hour or two that day, it certainly should have been near-full.

I DO have some excess electrical draw on the system - my cigarette lighter sockets are all wired to turn off after 30m of key out, rather than immediately when the car turns off. So that could contribute to long-term deeper-than-normal cycling, but certainly not short-term since-i-turned-it-off-that-day drain.

So Q #1: Is this a normal failure mode/degredation mode for an AGM battery? I would have expected CCA to test way, way lower if a cell was failing, for example.

Beyond that, I've had code 2DEB - "power management network failure" (according to Carly) for a while. I just for the first time looked that up in Bentley and the book says that 2DEB is actually undervoltage or overvoltage. The code first started appearing when I was charging devices off a direct-wired socket I put in my trunk, so makes perfect sense (I also got codes for excessive current draw, which, of course, there was.) But even after clearing those, 2DEB came back without further excessive draw.

So maybe that's related to my typically low SOC?

Question 2: During operation, my system seems to operate at 14+ volts continuously. I didn't scope it, so that could actually be noisy and dropping below 12 with high frequency, but I doubt it. Have you ever had issues with a low SOC causing a rough running engine? I feel like that shouldn't be the case, as long as the alternator is also fully functional.

Basically, I wouldn't feel bad about swapping the battery out, but I don't have much hope that i'll improve any of my car's engine trouble.

[Efthreeoh]

You don't state what model E90. I'm on my phone so I can't see your sig. Unless it's a black case, it's not an AGM. At 9 years old, just replace the battery and see if that cures any ills the car is having. Electrical charging sounds in spec.

[alexwhittemore]

Originally Posted by Efthreeoh

You don't state what model E90. I'm on my phone so I can't see your sig. Unless it's a black case, it's not an AGM. At 9 years old, just replace the battery and see if that cures any ills the car is having. Electrical charging sounds in spec.

Ahh fair - it's a 2009 328i, N51, black cased battery. I probably will anyway, it's just one more $200 part in a long list of $200 parts-that-probably-aren't-the-cause-of-my-woes

[robthewrench]

Look at it this way, if you plan to keep the car at least another year and the existing battery will probably die within that year, why not replace it now? A battery usually lasts at least 5 years, and you might own the car for less than this. Why not get the battery now and not have to deal with a battery problem in a year or so?

[GEOS07335i]

Batteries that are on thier way out tend to cause multiple gremlins in our cars. I just got done replacing mine for $100 with a walmart battery. It was close not exact match. Also i was able to reset it with MHD. If it's diffrent amp hours you will have to also code it. It's not a too difficult job as a DIY try and get an exact match and you just have to reset it instead of coding. Exact match would be more expensive especially if you go OEM. But regardless if it's 9yr old battery time for a replacement.

The way I could tell when mine was going was clock would reset and my convenience key option would not work if the car sat for a day or two. But if I drove around for an hour it would work fine. Change your battery and you should be good to go.