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Old 09-17-2014, 08:17 PM
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Join Date: Oct 2013
Posts: 126
battery drainage

My 86 300sl has a battery that's about a year old and granted that I don't drive it very much I went to start it last week and the battery was dead. I charged it back up and it lasted a couple of days and I went out to check it and it's dead again. Is it possible for lack of driving? Any help would be appreciated. Thanks.Greg. P.S.The clock doesn't work would that be an issue?

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Old 09-18-2014, 05:07 PM
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Join Date: Jan 2012
Posts: 7,515
The battery should hold a charge for months if there isn't something draining it. Clocks take near nothing but, if it is a old style pulse solenoid type, it might remain energized if not working, in any event I'd unplug.

Do you have access to a clamp on amp meter? If not, disconnect one battery cable then place a 12 lamp from battery to cable. If the light is bright, start pulling fuses until the light goes out to isolate what circuit the drain is in.

If the light never goes out, disconnect the large wire on the alternator, then the small one. A shorted diode in the bridge or a regulator that stays on can cause a drain.
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Old 09-19-2014, 11:21 AM
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Join Date: Jun 2013
Location: PNW
Posts: 242
Troubleshoot with an amp meter. See which circuit is drawing electricity when the car is off.

If you don't know how to do that, take the car to a mechanic who specializes in automotive electrical work. Many regular mechanics do not understand electrical troubleshooting very well.

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