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Battery affected by key left in car?

Discussion in 'E60 (2004-2010)' started by kenhasting, May 4, 2013.

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    2009 535xi. My battery went dead while I was sitting in a car wash listening to the radio. After jumping, the car seems to run/charge fine. A friend suggested you can run the battery down by leaving a key in the car a long time while car is off. Is this true? I never leave the car undriven for more than 2-3 days, and, in Montana, just starting the car means at least 30 minutes driving. Why did the battery run out?
    How do you find out if the battery needs replacement BEFORE it goes dead. I'm 150 miles from a dealer.
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    steven s

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    I kinda doubt the key or even having the radio on had anything to do with it other than the battery is getting old.
    Is it still cold by you?

    I suppose someone can test the cells but I'd probably just replace the battery for piece of mind.
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    Any auto parts store should have a battery tester for a lead acid battery. If you have a black battery it is a AGM and will require a special tester to see if it is bad. Your battery must have already been low on charge before you listened to the radio and that finished the rest of the charge off. If you leave the ignition on the vehicle will discharge he battery. Also even if the vehicle sits locked and unused it is still drawing on the battery not big around 40 milliamps or so. I would recommend getting a battery tender to charge the vehicle every so often. Also if you do replace your battery you need to get it registered by a dealer or it will kill your new battery fast.
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    Thanks for the input. This is my 4th BMW, the last 13 years of which have been in Montana where there is no dealership. This is the first time I'm faced with driving 200 miles to get a battery change and it makes me wonder if it's time for a BMW divorce. Audi may win out on this one, and that would be really sad for me. IMHO this is a classic case of overengineering.
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    I don't know when the 'comfort access' feature was introduced, but if you have that and leave the key fob in the car, the car won't enter 'sleep' mode, and the stationary battery draw will be higher, perhaps substantially, than when the car is, uh, sleeping. Check your car's production month - it may have been made as early as springtime '08; in which case a 5-year battery life might be about what's to be expected. If production was 12/09, about 3.5yrs sounds to me on the short side for battery life, but perhaps not unheard of. I've had a mechanic friend comment batteries of recent years have been cheapened compared to older batteries - less plates, etc, have gotten new batteries that were already dead, and not as long-lasting. To whatever degree that may be true, it may mean keeping recent-era batteries properly charged and conditioned is ever-more crucial to ensuring their lifespan. If you drive the car seasonally and the car sits out the winter in the winter cold temps without using a battery-conditioning charger, seems plausible to me that might have shortened battery service life. If you do like your car and would prefer to keep it, I'd say determine as best as possible why the issue's happened before throwing the baby out with the bathwater. But, yes, compared to what we've been used to, just popping out the old battery and throwing in a new one, adding on the battery registration procedure is one more unwelcome nuisance. Best I can tell, it's to optimize the car's ability to utilize the battery's power and maximize battery life. Being some distance from a dealer, perhaps it would be worthwhile to purchase the type of battery tester needed for peace-of-mind, particularly if your usage is seasonal. And, I wouldn't be surprised if this battery-registration stuff is something the rest of the Germans may have adopted also (or will), so if you opt for something else, check what's entailed with their batteries.

    Here's some info on AGM batteries:

    also -


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