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erv77

Battery drain tips pls

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2001 530i touring. Got the click from the starter motor, jump leads and it started fine. Battery is a year old. With engine off it was reading 11.26v when running I get 14v so not the alternator (must have been changed as sticker has 2009). Went for a drive, turned engine off battery reading 12.30v, cranked fine so I'm guessing it's a battery drain. I changed the FSU (and yes, OEM from C3BMW!) a few months ago. They say unplug it overnight, but in the cold, dark and uncomfortable 7 minutes it took me to unplug it, battery voltage dropped from 12.30v to 11.88v. Any ideas of suggestions mist welcome. On the plus side, my e39 last broke down over two years ago with a well overdue rad replacement!!

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currrent clamp on the battery cable

open tailgate and push lock across, do the same with front passenger door jam the door switch

let the car go to sleep 16 minutes

look for current drop as you pull fuses

car should be less than 50ma asleep

 

mine so far has been the webasto and the nav randomly waking up

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Cheers buddy, will try that. Since I've disconnected the FSU it has dropped from 11.88v to 11.35v so guessing something else is also draining the battery!

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voltage at the battery is a combination of how discharged the battery is and how much it is aged

using a voltage ref at the battery wont get you very far at all in this situation, apart from to tell you you need to charge it up again

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True, it's the drain which more important and that's measured by amps. I'm not very techy so I'm dreading how I get the bottom of the issue!

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Faulty battery, it's dead! Only 9mths old, listed as a BMW battery but they now tell me they wouldn't recommend fitting it to a beemer. Moral of the story don't but a powerline battery even if it has a 4yr guarantee, royal PITA as I have to send it back!

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Hi Mate, thanks for all your help on this. Turns out the battery was fine - it hadn't fully discharged and when it started I put it on charge in the garage. I was trying to work out how to test for abnormal drain and in the end I pulled both the FSU and the tow bar electrics fuse. No more drain. Plugged the FSU back in (as it's only a few months old and OEM) - no drain. Never towed and don't plan on it so not bothered about fixing the electrics - just leave the fuse out - hopefully I got lucky, but the car was sat for a week and fired up without hesitation!! thanks again

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