Battery Maintenance Question - Mercedes-Benz Forum

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post #1 of 2 (permalink) Old 04-21-2010, 06:33 PM Thread Starter
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Date registered: Oct 2002
Vehicle: 300 SE, 560 SL
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Question Battery Maintenance Question

I had my 560 SL connected to a bettery tender since putting it in storage last November. Although I never started the car, I did check periodically and the green charged light on the tender was always lit. Yesterday, when I tried to start it, battery was dead. Found out the extention cord was not plugged in! Battery is maybe four years old. Why would a battery go completly dead in six months? Normal?
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post #2 of 2 (permalink) Old 04-21-2010, 09:48 PM
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The battery tender led already must have consumed power from the battery if the cord was not plugged. If it was e.g. a 10 mA led (one can be sure that it is not driven with a switching, high efficiency supply), this would make 0.24 Ah per day, 7.2 Ah per month and 43.2 Ah per 6 months. Add internal battery leak and your battery is flat even if it had more capacity than 43 Ah.

A modern car with alarms and electronics can consume 80 mA (without the battery tender led), this would make 345.6 Ah per 6 months. No car has this big battery. I guess this is a 107 and would not drain 80 mA unless it had something wrong but if it had an alarm or even a modern radio, the battery would run out within 6 months. If it had no alarm and an old radio with switched power only, it might survive 6 months in case an unplugged battery tender was not connected.
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