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Hello all! I’ve owned my SL55 since new in 2004, only have about 14,000 miles on it. Over the years I’ve replaced the consumer battery a few times, and have it on a Mercedes tender from when i got the car new. Yesterday I decided to take the car for a ride and tender was plugged in but consumers battery was dead. I drove it for about 80 miles and on the ride the battery came to life, but I got the offline message a couple of times while driving. This battery is about 4 yrs old, do you hunk the charger is junk or the battery needs to be replaced?
I used to have a 2005 SL600, still have a 2009 SL600 plus a 2018E63S, which uses an underhood AGM battery as the main battery. I have a lot of experience with them. The trickle chargers can help but all they do is treat the symptoms and ultimately the battery will fail. I have a trickle charger but do not use it If the car is driven for a half hour or more almost every time it is used the battery will not have any early life problems. Most of us do not do that. What is needed is a high performance micropressor controlled charger designed for use with AGM batteries. These chargers include specific programs for running a desulfation cycle when needed to restore the battery. The one I have is a 100A unit made by Schumacher, there are others.
When you first get the consumer battery message connect the charger. it will likely go through the desulfation mode which can take two hours. wait two days and do it again, then a third time two days after that. The battery should then no longer give the message unless it sits unused for more than one to two weeks. My 2009 SL600 AGM lasted 8 years until I changed it. The 2005 lasted 6 years but the car was 4 years old when I bought the charger. The E63S just gave the first battery message a month ago. I ran it through the charge routine 4 times. I let it sit 2 weeks w/o using it. Started right up with no battery message. The message seems to be triggered when the battery voltage drops to 11.8V.
A 4 year old battery should be salvageable for at least a couple more years, but at this point not with a trickle charger. That is a short summary of a lot of trial and retrial of working with the AGM batteries. Good luck, these consumer batteries can be a real PITA. The good part is with two batteries the car can always be started.
On an R230, I don't believe the consumer battery from the factory is/was an AGM. The Mercedes trickle charger, if operating correctly, is good for maintenance but not so much for the restoration of a battery (some good options on Amazon for that).
Odyssey batteries are serious performers and with FCP's lifetime replacement plan, this will be the last consumer battery purchase your SL55 will need.
Here is a picture of the MB factory R230 battery. It is a VRLA (valve regulated lead acid) design. Of the two versions MB used the AGM rather than gel cell. The proposed alternate replacement above might be a better choice today but I have never personally tried one in the SL. If someone has used these in an R230 it would be great to hear the experience to date.
I had a “battery tender” branded tender in my garage that I used over the winter for my jet ski, plugged it in and next day the light was solid green indicating over 80% charge. We will see how it goes
I have an Odyssey 48-720 consumer battery in the trunk of my 06 SL65. This car has a 40ma parasitic discharge. This is a considerable discharge for the battery to deal with. This discharge rate will kill the battery in two weeks. A battery state of charge below 70% will sulfate the plates in the battery causing permanent damage. I have a Battery MINDer hooked via pigtail to the consumer battery anytime the vehicle is parked. As you know the starting battery only turns the front starter. It does not even engage the solenoid. This battery is recharged at a rate no more that 15 amps via the module in the trunk. I have had excellent service from the Odyssey batteries in my ML, SL, and CL. In the above picture I would sure like to see a fuse on the small red (+) wire coming off the battery. As an aside Halon fire extinguishers are my favorite. The service manual has a nice writeup for preparation to measuring the parasitic draw.
A happy electrical system is a wonderful thing. I would be happy to hear your results.
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