Our BMW 325xit (E46) wouldn't start the other morning. ODBII readout was showing very low battery voltage. Jumped it and it ran fine, so off to Wal Mart for a new battery.
With a brand new battery it started up, but it was a bit of a weak start, didn't crank very hard.
It survived a 15 minute drive, then 2 hours parked, then 10 minute drive.
The next morning it was dead again.
I jumped it and took it for a good 40 minute highway drive. Stopped the car for about 5 minutes, got back in, weak start again.
When I turn the car off the voltage is showing about 13.0V. When running it's 14.1-14.2V (So alternator seems good?)
After a few minutes the reading is down to 12.7V.
I have no symptoms of a bad FSU/FSR.
Is it possible the battery wasn't fully charged when new and just needs an overnight charge? (I've read it can be 10-12 hours to fully top off a battery, and driving only really replaces what you take out to start it)
Could I have some crazy parasitic drain that popped out of nowhere? For it to drain that fast seems insane to me, but who knows.