JayArras

I'm having issues with my 530xi turning over slowly if I don't drive it for a few days. It's fine if I start it every day, but it seems like the battery is losing juice over time. I'm not getting any High Battery Drain messages or anything like that. Is there a way to test whether the alternator is charging properly?

advancedlogic

Is that the original battery? If over 2 or 3 years old, suspect it. Buy a voltmeter (accessory socket unit would be easy for convenience), charge the battery charged, and check the volts before starting or turning anything on (should be, at a minimum, around 12.6V @ 80 degrees or so. Drop roughly 0.01 for every 10 degrees F). If rest volts are OK, start the car. Volts should climb to around 14.5 or so (if it drops or stays in the 12's or even low 13s, you may have an alt issue).

A simpler method is to drive to Pep Buys, Advanced Auto, O'Reilys, etc, check the running volts, and to a battery load check.

Only Bimmers

The easiest and proper way to check both is the following.

Charge the battery independently of the car and bring it to your local autoparts store for testing. They have high end digital analyzers that test many things and will tell you exactly what is going on. It is very granular so it can detect many different faults in the battery.

If that checks out good return all items to normal in the car. Use an analog multimeter ont he battery terminals ont he voltage setting and monitor the needle. You should see well into the 13-14 volt rand depending on what you car is drawing. Look at the needle and see if it is wildly fluctuating. This would mean that the alternator is seeing some kind of issue. I would then remove the alternator and bring it to the same auto parts store as they again have a digital analyzer for that as well. They spin it up to normal idle rpm and test it thoroughly. It will save you allot of $ if you spend some time.

westsidebalto

If he doesn't have a multimeter, would the secret menu work for getting the voltage?

turboawd

by the way you described it, i'd say battery. especially if its more than a few years old.

JayArras

My car is an '07. It has the white FLA battery with the German markings, so it could be the original. I'm the second owner, so I can't be sure.

BTW, after I posted my original post at 5:22 PM, I got the High Battery Discharge message for the first time on the way home from work. When I shut off the car and restarted it, the message went away.

turboawd

the original batteries have the date of manufacture stamped on top of the negative battery post.

BimmerFan52

Easiest way - Remove the battery and/or alternator from the car?
You're joking, right? Removing and replacing the alternator on a BMW is not a trivial 15 minute job (on a 545i try about 3-4 hours for an average DIY).
Both the battery and alternator can be completely and thoroughly electrically tested without removing them from the car.

OP - From your description the main culprit is your battery chemically failing (remember the battery holds no "electrical charge" but instead chemicals that when a load is applied release electrons through a chemical reaction) or a parasitic load is discharging the battery over several days. When you drive it every day it stays charged. The alternator is therefore at least doing a minimal job.

That is not to say your alternator (or more likely voltage regulator) might not be in the early stages of failure and not doing a full job of charging. But it is at least partially charging the battery when used every day.

Also, when the voltage regulator on the alternator is in failure mode the voltages sag low and can also swing wildly high and low. This can cause the ECU and CAS to begin to shut down non-critical loads such as interior lighting and then later computer modules (transmission control module, active steering, etc.) to prevent low system voltages from driving over current situations. When multiple computers shut down the dash can start to light up like Vegas at night. If you are not seeing any of these symptoms, but the car just doesn't start that again points to the battery.

As advancedlogic said, go to the Auto Store and they will test the battery and alternator with a hand-held computer and tell you what is going on.

JayArras

That still doesn't tell me when the battery was installed. A replacement manufactured months/years earlier could still have been installed later.

JayArras

That sounds like the most logical next course of action. Thanks guys! I'll post back when I have the solution.

BTW, Advance Auto Parts won't touch the installation of a BMW battery, even though they advertise it as a free service (which I guess is a good thing.)