A couple of weeks ago we drove about 2 hours on the highway and then exited to secondary roads for the final 7 miles to our house. The R500 seemed fine until we got off the highway. At slower speeds it seemed to lack power, sluggish. It eventually dawned on me that it wasn't downshifting. When we eventually came to stop at a light, the engine stalled. I assume because the torque converter was locked and the transmission was stuck in one of the higher gears.

Tried to restart. Nothing, wouldn't even crank. I finally removed the smartkey then re-inserted and tried again. Success, it started and the transmission began acting normally for the remaining 5 miles or so. I figure, oh crap it's the conductor plate which has supposedly already been fixed once.

So I park it in our driveway for a few days and drive the SLK55 until I get around to calling for a service appointment. Saturday, I go out to start the R500 and move it so I can mow the lawn. Nothing. Completely dead electrically. It wouldn't even respond to a jump start. So, I figure what the hell and put a trickle charger on it for a few hours. Success. It cranks and starts but the battery seems weak. But the trickle charger flashed a bad battery message after only a few hours.

Before someone mentions it, no the drain isn't plugged. Everything is dry inside. And the blower motor is not running amok.

And according to the service history, the battery had been replaced twice before I bought the car with 36,000 miles. The car now has about 41,000 miles. Three absorbed glass matt batteries in 6 years and 41,000 miles seems ridiculous.

So something seems wrong here beyond a battery. Battery cable? Alternator? Voltage regulator? Can the conductor plate short and drain a battery?

At any rate, I'm having the car picked up by MB roadside assistance. Not gonna try and drive to the dealer. The dealer agreed with that approach.

And I think that I'm going to buy an Autozone battery as a replacement. Mercedes wants $240 for their wondrous 2 year life AGM battery plus installation of $150. Autozone is asking $170 for their own AGM equivalent and I think I can handle the seat removal.

We'll see what this costs Mercedes but I'm certain they will try and squirm out of a battery replacement no matter what the cause.

 

Keep in mind if you need to have your battery replaced, have it replaced via roadside. They don't charge you for labor and the battery price may be cheaper than the dealer. (and they do it at your house!)

 

Thanks, I may try that if I need to. But I looked at the service records today and the last replacement battery was put in the car 08/28/2012 @ 33,614 miles. So it's only a little over 8 months old with about 6,500 miles of use. I believe Mercedes has a 2 year replacement warranty on their batteries. I should get a free battery out of them. No?

My real worry is why 3 batteries in 6 years / 40,000 miles? No absorbed glass mat battery should die in 8 months even if the car is in a fleet being driven 24X7. Nor should they average roughly 13,000 miles. I can live with a 4 year life. This car has beaucoup systems drawing electrical energy. But 8 months? Something's wrong. And why the battery failure immediately following the transmission failure?

 

its not the battery. The Rs seem to have a current drain somewhere. I had my battery replaced winter 2012 becuase it would not start after a few days parked. THey did not find the current drain. Happened again this winter, Stuck at the airport parking. This time they did find a current drain in a rear parking detector.

 

The battery may not have been defective. I doubt that it was. But whatever current drain left it without a charge seems to have damaged the battery. My battery charger ran for a few hours and then displayed the message "bad battery" meaning that it was unable to fully complete the charge cycle.

 

Well, I called MB Roadside assistance this morning and the R500 is off to the dealership on a flatbed. I stuck a copy of the service history on the front seat showing the battery replacement Aug 2012 plus the former attempt to repair the transmission valve body and conductor plate along with a copy of the TSB for the conductor plate.

Lets see what they come up with. I also told the service rep over the phone that I tucked the service records in the car and that the car is dry as a bone inside just in case they try and pull the old "plugged drain" excuse for the discharging battery.

 

Dealer called at end of day yesterday to inform me that they didn't get to my car. No problem there as mine was a no-appointment last minute delivery via flatbed.

But the service advisor seemed a little peeved that I stuck a copy of the service history on the front seat with the battery replacement date and the former transmission repair highlighted in yellow marker.

Seemed even more peeved that I left him a copy of the conductor plate TSB along with Mercedes email to dealers about handling warranty / non-warranty repairs.

C'est la vie. I'm not looking for a new friend. I just want the dealer to know that I know at least a little about Mercedes well documented problems relative to the 7G-Tronic transmission circa 2006-2007 and the fact that the car has devoured three AGM batteries in 40,000 miles.

 

Well, Mercedes has had my R500 since Tuesday. 5 days and counting. They said I'll likely have it back Tuesday. So, 8 days. They are definitely replacing the valve body and conductor plate. Second time replacement for this car. They said that's about a $1,600 repair. But they don't have any verdict on the dead battery. They are having problems with software once they replaced the transmission hardware. Now trying to get all the software on the same page and ECU, TCU, and whatever other computers are involved talking to each other.

They said once the car is running, they will have to check for electrical draw. But good news (I think) is that they say the battery checks out fine and holds a charge.

Meanwhile I've got a 2013 GLK 350 as a loaner. Weird little car. I can't find a comfortable driving position. Reminds me of driving a van for some reason.

 

Curious, how did they give you the GLK loaner car? Did they flatbed that to you and you traded for the R?

 

No, they picked up the R500 Tuesday morning in my driveway. I drove my SLK55 all week thinking the R would be ready in a few days. When it became apparent that this adventure was gonna stretch across a weekend, I went down there Saturday with my wife to pick up a loaner. I was already headed there Saturday as I had ordered a pair of gas struts for the trunk lid of the SLK. I was tired of getting bonked on the head.

That's when they gave me the ugly little GLK. I think it goes back today. They said yesterday that the R500 was back together but they wanted to run S/W diagnostics again and the transmission fix required a 30 mile road test. So, hopefully I get the white whale back today. Can't wait to see the total bill for Mercedes.

The reason I wanted a loaner on Saturday? I've only had the SLK55 for a few weeks. The dealer gave me a temp registration (20 days) and then waited until day 16 to hand the paperwork over to a 3rd party agent. I found this out with a phone call, day 16 when I called to inquire about the status of my new registration. Azzwipes! So, as of today the SLK55 is not legally registered. They tell me it takes their 3rd party agent 8 business day to process a registration. Great! If we didn't have more than two cars, I'd be walking. Sometimes dealers really do suck.

 

Well, I got the R500 back last night. New valve body and conductor plate. They also did the transmission service, new fluid and filter, and told me the transmission service is good until 80,000 miles. The car seems OK. What a difference driving the R500 vs the GLK 350 loaner car.

As for the battery, they tested it and it's holding a charge. Checks out healthy. They also checked for current draws while the ignition is off and said they found nothing that would drain the battery. So, OK the battery drained for no reason in a week, was totally dead, and now is fine. Suppose I'll just have to wait and see if it happens again. Maybe it was somehow related to the transmission malfunction.

The total tab for Mercedes? About $1,700 bucks.