A Battery Story


Nov 24, 2017
Indiana, USA
Z4 35is, 535xi, X5 35i
After years of BMWs and several models, I experienced a new problem that I didn't recognize.

Started the X5 in the cold morning. It has had a bit of a slow crank in the cold but always starts just fine and no clock resets, no high discharge battery warnings. I know battery needs to be on the list but nothing making it seem critical.

Drive the X5 20 mins to an appointment, come out an hour later and start it up. It turns over nice and strong but doesn't start. Try again, starter and engine cranking over fast and strong but no start. This time start to get a slew of idrive warnings and decide to have it towed in.

Diagnosis was bad battery. But the strong cranking and turning over via the starter motor did not make it seem like a battery issue at all. Never did get a clock reset.

In retrospect, we did get some weird behavior on the drive over. When we attempted to control the HVAC fan manually, it would not go to a higher speed but if we put on the windshield defrost, the fan went to max. After the battery was replaced, the HVAC worked as expected.
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General of the Army
Oct 18, 2016
2009 E93 335i
I've learned this as well. Unfortunately, BMWs can be really picky about the battery condition and it defies traditional troubleshooting processes. I once drove around in a car that had the BST severed partially. Trying to figure out what was going on took quite a while and left me stranded one day. Turns out hitting the brakes would shift the battery around since the tie-down wasn't secured and the alternator could charge it again eliminating issues that seemingly came and went mid drive.