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This is driving me crazy. 405 has a new-ish battery, but if I don't drive it every few days, it'll be dead when I need it. No clicking, no instrument lights....nothing. A quick charge and there we go. Keep this up and I'll be buying another battery in no time.

In recent months....

- new starter

- checked wiring to starter, alternator, etc.

- alternator working right.

- inserted ammeter between battery negative post and negative wire. Meter shows drain of about 8 mA when everything is off. YouTube instructional videos say that's ok.

- inserted ammeter between battery positive post and positive wire. Meter shows drain of about 8 mA when everything is off.

- removed each master panel fuse in turn, meter shows no substantial difference.

- Parked in a dark garage, so I should be able to tell if any lights are on, etc.

Any ideas what I can try now?

f s

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Is the car completely dead with no signs of any life?  Battery voltage when it’s like this?  Do the headlights come on?  

Have you disconnected the battery for the same duration to see if the problem remains when you reconnect?

8 mA is well within spec, but just make 100% sure it’s not 0.8A...  :)

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I'm dealing with a bad battery now on my 607, i've also been thru all the diagnosis, its simply a bad battery, try disconnecting the negative terminal when not in use as Bean said, also try removing the radio fuse if you have a aftermarket radio, In all my years i've seen 3 things that cause battery draining issues, 1 failed electronics newer vehicles, digital dashes, 2 aftermarket radio, 3 partly failing alternator, one or more diode in the alternator is letting electricity to feed the alternator, very hard to diagnose, when it happens, on a cold day with a flare camera you can see the alternator is warm, but by hand is very hard to tell especially on the my 16 because is covered by the intake manifold partly.

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  • 2 weeks later...

I just helped a friend diagnose his BMW 335d - Ended up being the rad fan relay was energizing when the fuse was in. When he checked the relay it was warm, and it was consuming at least 300mA with the car off and fully asleep.

Strange one indeed - but was found using the ammeter between negative post and negative cable while he pulled fuses.


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