Taking a poll-convenience battery - Page 4 - Mercedes-Benz Forum
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post #31 of 33 (permalink) Old 12-21-2016, 04:49 PM
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Date registered: Oct 2009
Vehicle: 2003 SL500
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Originally Posted by tonyjroy View Post
I left the battery hooked up the entire time

Ahh ok, thanks, I was concerned with the way it does the descaling by adding extra voltage, I did not want to burn up my BCM
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post #32 of 33 (permalink) Old 12-24-2016, 02:51 PM
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Date registered: Jan 2011
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I'm not getting convenience functions unavailable message but often after the car has been sitting they don't work. If i try to tun on the heated seats the lights just blink and nothing else happens. But the biggest problem is that the top won't go down! I have to drive for awhile and restart the car before it will work. Could this be a battery issue? I think I replaced both of them a year or two ago.
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post #33 of 33 (permalink) Old 03-03-2017, 01:37 PM
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Cool Convenience Battery.....Just my problem solved.

My SL600 is serviced by a local independent, Luxury Auto Works. Lucky for me, the owner is a 30 something mechanical dynamo. This guy lived in Germany and worked at Benz factory. Most of his 20 something certifications were on my 2007 SL600.

That said, this guy knows my car inside and out.
He solved this "convenience battery" issue for me in less than 30 minutes.

He connected a volt meter to the battery in the trunk and I watched the voltage fluctuations as he cycled through various convenience modules (AC, Heated seats, Radio, CD Player) etc. As the engine is running, he was loading the electrical system to see if the alternator was able to keep up with the demand. Turns out the alternator was not providing a constant, stable voltage to the battery.
I forget the exact spec, but the alternator must never drop below a certain voltage under a heavy load.

The alternator on these cars are water cooled and require some technical expertise to replace without recurring issues.
That said, this was an expensive parts and labor repair. The cost of a new water cooled alternator was $1,430.00.
I was skeptical this would solve the problem, so this was his response.
"If this does not resolve the issue, I will refund the full cost of parts and labor." "In addition, all parts and labor have a three year, 36,000 mile warranty." That's all I needed to hear.

Such a simple and basic trouble shooting exercise.

Well, it's been six months and these issues are no longer a problem. I travel, so on occasion the car sits idle for up to two weeks with out any exercise.

Just wanted to share this information and maybe provide a starting point for others with this issue.

Cheers and happy motoring!
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