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1994 e320 cabriolet, keeps draining the battery. I've had…

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1994 e320 cabriolet,...

1994 e320 cabriolet, keeps draining the battery. I've had experienced Mercedes guys work on it, fixed bad grounds, replaced the battery. Alternator puts out 14.5V (measured at the cigarette lighter). Drops to 13.3V with the lights on. Never below 12.6V.

Mechanic's Assistant: Did you test the battery with a voltmeter? And have you ever changed one before?

Seems to run out over night with no key in the ignition and nothing turned on. Only way to stop it is to detach the negative battery cable.

Mechanic's Assistant: Are you fixing your E320 yourself? What have you tried so far?

Yes, those voltage readings are from a volt meter. I've put 3 new batteries in this year.

Mechanic's Assistant: Anything else you want the mechanic to know before I connect you?

I am fixing it myself because I tried 3 mechanics and they didn't fix it.

Submitted: 8 months ago.Category: Mercedes
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Answered in 12 minutes by:
9/20/2017
Mercedes Mechanic: Marty, Mercedes Technician replied 8 months ago
Marty
Marty, Mercedes Technician
Category: Mercedes
Satisfied Customers: 55,103
Experience: Bosch Certified Master Tech. Over 35 years experience.
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Hi, my name is***** need to do a systematic diagnosis of the drain. Disconnect the negative battery cable and place an ammeter between the cable the the battery post to measure the amperage drain on the battery. Anything over 50 milliamps is too much. With all doors closed and everything turned off in the car you then need to start removing the fuses from the fuse box one by one until the drain drops to an acceptable level. When your drain drops, you have located the fuse circuit that is draining the battery. From there you need to check the items on that circuit for your drain. A bad alternator can also drain a battery overnight.

Let me know if you have any questions.

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Mercedes Mechanic: Marty, Mercedes Technician replied 7 months ago

Just checking in. Do you need any more help with this?

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Mercedes Mechanic: Marty, Mercedes Technician replied 7 months ago

Anything?

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