What's the easiest way to connect the SL63 AMG to a trickle charger? I know that many brands these days can connect directly to the 12V outlet in the car, but I also know that this doesn't always work for all Mercedes, and some Mercedes models require you to connect directly to the battery.

Curious what people here are doing.

 

Don't connect to the 12Volt outlet. Manual says NO. Under the hood at the firewall on the passenger side there's a horizontal "door" that lifts up. That is where the positive connects. Slide the tab to reveal the connection point. Then the negative connects to a post a few inches in front of it. Clear in the owner's manual. Search on this site and you'll see a thread with photos.

 

Or you can connect to the battery terminals directly from under the panel in the trunk. Given the ongoing concerns with the 12v battery losing its charge, the shop at my local Mercedes dealer connected a new Mercedes trickle charger directly to these terminals for me, leaving just the connector/adapter on the charger wires available for connection to the charger itself whenever I felt the need to plug it in for charging. I also think the trunk location is better than from under the hood, as the rubber gaskets around the trunk are soft enough to allow the wire to pass through to the outside without crimping it too much. See the photos.

Red wires from trickle charger connected to battery terminals

With truck compartment cover closed and leads connected to charger with plug adapter

Trickle charger disconnected with just adapter exposed

 

It is worth noting that if one specs the car with the Trunk Kit it comes with a 12Volt outlet for trickle charging. Like my GTS and GTC had!

 

I had a significant battery issue to start but I think they have got it better; not sure it's perfect, but better; they also provided the direct to battery connection and gave me a free MB battery/trickle charger.

 

So how long can you really let the car set without a trickle charger and expect everything to work properly? I frequently go 5-7 days without driving my car and would hate to think that I have to hook it to a charger every time I use it.

 

I was in India for over three weeks and when I returned I had no problem. Here is what I did. Before I left I made sure the car was completely charged and then I double clicked the key fob to lock the car and I removed the key fob from the vicinity. This was so there wouldn't be any communication between the car and the key fob. At the dealership they suggested about 20 feet. That was easy. When I returned the Mercedes app showed "partially charged" and the car started up just fine and ran perfectly. Apparently one of the issues is it the car and the key fob like to stay in communication and if we keep them out of range the car has much less drain. Of course there is some other main software issue. Mercedes seems to believe that the Mercedes Me application is poorly written and it throws up a lot of unnecessary battery messages which freak people out. Understandably! But what other issues there may be I don't know but it is telling that I was in India for over three weeks with zero issues when I returned related to starting the car and running the car. One key is to always keep the car locked and when going away for longer periods of time remove the key from close proximity. I told the dealership how ridiculous it is that one drives into their garage and must lock the car. They agreed - but until there is a hardware or software fix of some sort these are mitigating measures we can take.

It is also interesting that no matter how many times I've had dire messages about the state of the car's 12 V starting battery, the car has never failed to start and run just fine. Nevertheless, the onslaught of varying messages of battery condition can be disconcerting without the ameliorating knowledge that the car always starts fine. At least it has for me.

 

I've been fairly lucky in terms of the ongoing issue of battery drain and associated warnings, but last week I got the dreaded warning that the battery was in critical condition. It was weird as I had just driven the SL the day before for over an hour at speeds in excess of 70 MPH. Anyway, I put a trickle charger on it and it's been good to go since. But as California John states it can be disconcerting. I have not reported this issue to MB as I have not had the car in for service yet but obviously they need to hear about the issue from everyone so they will have a sense of urgency to resolve it.

 

True. All need to report it. I've had the critical a number of times. Still started and all was fine. But each time it has been after longer periods of little driving. To have it the day after an hour's worth of driving at good speed just shows how screwy it is.

 

I've had a few issues when the battery was critical involving some functions in the car not working on startup and when the car was at the detailer they couldnt get the battery to hold a charge but htye had the doors unlocked and the key closeby. I've also discovered that sometimes the battery isnt fully charged when I hook up the trickle charger and takes a half day to fully charge. For now, I guess it is what it is as long as I dont get stranded somewhere.

 

sure? I have that option and that would be even easier

 

This is from the MB SL63 Build Page. That is really all I know. In the GTS and GTC I had, each had a 12 volt power socket...but none of the other amenities listed here - if I remember correctly. When I spec'd those two cars I definitely did not order a "cargo system for trunk" - don't know if they were available.

 

It would drive me insane having to lock the car every time in the garage at home. Plus we keep our keys in the kitchen which is probably 20’-30’ at most.

 

I just accepted it and got used to it. Our garage connects to our kitchen and the keys are just 5-10 feet away from the car. It's no problem. I only put them a good distance away when on an extended trip - as a bit of insurance,

 

I was told by a Mercedes salesman at a different dealership than where I subsequently purchased my car that the R232 SL 55 had a lithium ion battery (which I had in my 992 911 and absolutely hated). I have a CTEK lithium battery maintainer at home. I'm no engineer but I'm pretty sure this picture I took of the battery in the trunk of the SL is a lead acid battery. Can anyone confirm this? I just want to make sure I connect the correct CTEK battery maintainer. Sorry for my ignorance. Thanks.

 

Since the battery’s ID label specifies “AGM” (Absorbent Glass Mat), as well as “Pb” (the chemical symbol for lead), I think you're right to assume it’s a lead acid battery.

 

Thanks!

 

Definitely a lead acid battery of the AGM variety.

 

There have been posts that suggest that, in addition to the large AGM battery under the trunk, there’s a lithium ion battery under the hood, perhaps underneath where the positive charging terminal is. There’s what looks like a motorcycle battery-sized box under that terminal. I haven’t been able to confirm that. If that’s the case, it may explain the critical battery messages if they refer to this small battery. Parts diagrams online haven’t revealed the truth, unfortunately.

 

The under the hood terminals you see are not to a lithium battery that is located there. Rather, these are just jumper connection points that are connected to the 12v battery under the cover in the trunk. This is clearly stated and shown on page 324 of the manual in the section on breakdown assistance.

Page 324 of Manual

 

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Thanks so much for the information. Do you close the trunk tightly after you connect the trickle charger ? Or do you just put the trunk lid down but not close it all of the way ? Thanks.

 

I close the trunk lid all the way. There is a fairly soft gasket all the way around the opening, which gives way sufficiently for the small gauge wires. I wouldn't want to risk leaving the trunk slightly ajar and having a trunk light stay on or the car not detect it is locked properly, which is something you should also do to conserve battery drain.

 

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Thank you very much for your help & advice !!!!

 

Thank you. I was aware of these jumper terminals and use them with my battery maintainer. There has been a persistent rumor/myth in various forums, or maybe fact, that there's a 12V lithium ion battery somewhere in the car. The sub-trunk battery is pretty big and the critical battery messages make no sense, leading some to believe that the mythical or real lithium ion battery is the one that's suffering panic attacks. It makes no sense to me to have two batteries with different chemistries, so I concur that the one under the trunk is the only one.

 

I've had the 2022 AMG SL55 in the shop numerous times for Critical Los Battery. I've tried all suggestions within these posts (thank you) for double locking, key over 20 feet away from the car, etc. I have a seasoned service advisor and a sophisticated high-volume dealership, and they have no fix. In last week's service, they replaced the battery to which I drove home from service, and four days later, I started receiving the Critical Low messages again. I had not driven the car in the four days since battery replacement with all the battery-saving suggestions listed above. The nudge in the back of my mind about it starting or not starting is confidence-shattering. The dealership tells me MB is now officially acknowledging the issue through a trickle charger assembly campaign (still trying to verify the campaign), so back to service we go. The service advisor suggested I simply plug the car in when in the garage. I would have purchased an EV if I wanted a car to plug in to use .