gsyukon

I have a 2005 SL600. I have been getting the convenience functions unavailable for several months, when I let the car sit for a couple of days. The other day when I left work I didn't get the error until I made a few stops, which it never happened before. I got home and put a volt meter across the battery terminals and was getting 12.8 volts (front battery) when the car was running, The back battery was showing the only 12,2 volts. Ok my thoughts it was the alternator, so checked into getting a alternator and about hit the floor. Never heard of watered cooled alternator. So today before I order an alternator I checked the voltage again and it was 13.9 volts across the battery when running, the engine was cold. Has anybody ran into this problem? should I be looking at something else? Any help would be grateful.








Thanks,






Gary

Plutoe

Before I purchased anything---I would have the battery system load tested--that you can't do with a volt meter. Then based upon the test I would go forward!!

PS: If you had an under preforming alternator your dash would light up!!

latemodel21

I am confused, your thread title mentions "...and low voltage at starter battery" but you measure 12.8 .

To be clear, your trunk battery is the consumer/convenience battery ... and the message after a few days of sitting is not that unusual for batteries that are older.

Having the message appear after a little driving is less common. In one case (on my SL55, 2003) I had the message come and go (like you are having) and I found that the CAN connection at my rear SAM (under cover where left rear seat would be if there were rear seats) needed to be reseated ... and the problem went away. This is the CAN bus connection that goes to the battery priority/charging module (module in trunk, forward of consumer battery). My guess was that the connector was never reseated properly after I installed the smart-top module.

However, your problem is MOST likely an aging battery (consumer battery, in trunk). Some owners make this a non issue by hooking up a trickle charger when not using the car ... but if you have not done so already, you should evaluate the condition/age of this battery and prepare to replace it.

Cheers,
Chris

latemodel21

if your alternator is acting up, consider pulling its regulator (mounted on back of alt .... on a v8 it can be removed while alternator is in place ... on a v12..?).

look at the brushes on the regulator ... they may be at the end of their life (they wear away over time). If you need a new regulator, take your old one to a Alternator rebuilder (so you are sure you get one that has the same connector keying ... as they are keyed differently for different applications).

The regulator can be had for as little as $100

Cheers,
Chris

cyglee

Another vote to replacing regulator. My V8 showed 14.2v on front battery, but only 12.6v on rear with engine running. Changed regulator yesterday and both batteries are charging at 14+. The old brushes were worn ~5mm compared to new. Hopefully, the V12 regulator is similarly accessible. Also consider changing batteries if they are getting old, low voltage readings will cause dash messaging.

Tommyboy928

should be 14,2 volt for correct charging. good idea have a trickle charger,if not use car often, trunk batteri is often the issue. But ANYWAY , everyone should charge that trunk batteri , driving often ,or long, just get the batteri up to 60 to 70 prosent , toppcharge sometimes is a good idea.

lawrence99

had the same thing happen to me.
I took it to dealer (CPO warranty) and they couldn't find anything wrong but said my convenience battery was over 5 years old and needed to be replaced.


I was going to put a battery in myself that weekend and next day stopped at gas station and it wouldn't crank. Gauges would just sweep and no crank.


Check the starter battery after sitting overnight < 10 volt


So I check the convenience battery also low. I shopped around for about a week trying to find a better price then the dealer on the battery and just kept a battery tender on at night. Finally just went to Benz and got a starter battery and all good. Three day later command starts acting funny... shuts down on it's own, looses blue tooth audio, ect.


So back to the dealer and they check it out and the command has errors on the hard drive. Talk to a Benz tech I work with and he tells me that the command hard drive can corrupt with a flaky battery.

As far as I can tell the starter battery is charged 1st then the convenience battery.


With a bad starter battery that will not charge up to full means the convenience battery doesn't charged.


moral of this story - do both batteries with OEM - pay the money - do it right and do it now.


P.S. the command NCT2.5 is about 3500.00 to replace out of warranty and has to be programed to that vehicle.

happypr

Just a little 411 , interstate batteries carries the OEM batteries for Mercedes. My starter battery was dying last year so, I went pricing checking and found the Advance auto and some other carried the battery but all were special order but I found , interstate had the battery in stock for a very reasonable price of $160 US plus another $20 to install. The dealer wanted double that, well when the tech brought the battery up, it had Mercedes OEM tags on it, made in Germany, apparently Interstate batteries is the supplier for the dealer !! So, try them 1st . My convenience battery is about 6 yrs old and I will be replacing that this fall before putting my baby away !! hope that helps !!

moretech

I have an interstate trunk battery which came with my car. It has never failed but is there any way to tell its age? I do not see any tags on it to help me determine that.

moretech