odd battery or startup

[dubtobimmer]

Hey guys, I have a 2008 328i rwd.

I have noticed that when it rains, occasionally when I start the car, the rpms will dip shortly and then save itself. Most recently I started the car and it shut off. Started it back up no problem and ran fine. Ive had the car about a month and it seems to only do this when its raining. I started to believe it may be bad grounding cables as this came up as a possible issue.

Today, it was very cold, and this morning the car started up, but just sounded a little slower than normal. The past few days have been cold and I noticed that the start was just a little slow, but still fine. Well I drove about 15 minutes and then my wife took the car. She said she was sitting in the car, with the key in but engine off, listening to the radio for about 2-3 minutes when the battery light flashed and the radio shut off. Now I know that its a safety measure build in, that the radio turned off. She was able to start the car no problem after she went shopping.

I got out the ole multi meter and ran some numbers. With the negative battery cable disconnected, in DC Voltage mode I tested to the +/- terminals and got a reading of 12.55 which I believe to mean that my battery is nearly fully charged. I then tested the voltage from the negative battery post to the disconnected negative battery cable and got a reading of 12.49 leading me to believe that in fact, the ground may very well be fine. Lastly I tested the voltage with the car running from +/- terminals and got a reading of 14.98, which tells me that the alternator is doing just fine as well. Maybe even over charging a little.

EDIT: I forgot to let the car sit before testing before. I ran out to get a battery for my multimeter and forgot, so I tested the battery itself again after 2 hours. Reads 12.33 which still is over 50% charged. However, I looked at the date stamped into the batter...25/08 the 25th week of 2008, meaning, this is the original battery....over 10 years on it. I tested the cranking voltage and it drops to 9.76 during crank. I have read that 9.6 is the magic number and below that it needs replacement. Im pretty darn close..Would you replace it?

So then if this is all true, why did the battery light come on this morning after running the car? Had about 4-5 startups since then and no issue at all, doesnt seem slow.

Anything else I should be checking? I still am questioning the grounding cables, due to the issue I have when its rainy. I just dont want to get stuck somewhere.

Thanks..

[rosakirk12]

10 year old battery is amazing. Multiple starts with little charge up time will be cumulative. I would be hesitant to travel out of town or to far from a free ride.


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[dubtobimmer]

Yeah...well this morning I tested it again..it was about 20 or so last night, so pretty cold. Before starting the meter read just about 12 dead on, which from what I can find, is about 25% charge. Car started up no problem and the crank draw was not less than 10v...but it seems like if I had done it even earlier, and colder, then it may have struggled. During the week I start it up at 7am...today, 1pm so its not as cold currently.

[rosakirk12]

Why don’t you just buy a new battery and not worry about it anymore.


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[jclausen]

We recommend battery's at 4-5 years. Yea the battery is to old, just from a maintance perspective. Plus it's cold out. But e90's can need a battery because it's just old and still have slow cranking because the starter is also worn out, seem that many times.

[dubtobimmer]

Well today I decided to replace the battery...upon startup with the new battery, the car died right away. Started up again no problem. I'd love to figure this out...in my head, I needed a new battery anyway since the old one was 10+yrs old. This starting issue seems to happen moreso when I start the car multiple times in a short amount of time. Ill start it and it will either die right away for the rpms will dip and then die. Second attempt always seems to be fine, but today it happened multiple times. Getting tired of it. Seems to run fine otherwise. Any ideas here?

[jclausen]

Did you ever have any faults stored

[rosakirk12]

Fuel Pump/filter/relay


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