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BMW battery drain

I own a 2003 BMW 5301 with the sports ,premium and ‘M’ package. Of late the battery drains for no apparent reason. This happened a few times 2 months ago and I had the battery and alternator replaced. This has again started happening. The car starts promptly in the morning but refuses to start in the evening when I am ready to leave work. It has to be jump started. This does not happen everyday and the BMW service folks have not been able to figure this out. Any help would be appreciated.

This can be a really tough one to figure out unless you can spot something obvious like a dome light that stays on when it shouldn’t.

Does it have an alarm? Sometimes alarms can be triggered by various events, like spurious radio signals or vibrations from a construction site, and then they sit there draining the battery.

That it starts fine in the morning, but not in the evening tells me there might be something about the environment in which you park it at work that’s causing a battery drain. You may end up having to park it at work and then test each circuit to see if one of them is using power.

For starters, I’d post back with details about where you park it (nothing that would identify where the car is to potential thieves, but what sort of lot, what’s around the lot, if any road work or construction has been going on in the area, if it’s a new parking area as of 2 months ago, etc)

My neighbor’s BMW had the same symptom.
Turned out one of the power adjustable seats was drawing a 6 amp pulse of current every second or two.
The cheap fix was to take a fuse out and only put it in when the seat needed adjusting.
You need to look at the battery drain with an ammeter.