I recently left my car in the garage for about 4 days. When I returned, and clicked the key fob, nothing!!! Thought it was fob batteries, but doors were unlocked and when I opened, no lighting or illumination inside. Called my mercedes tech friend, he says he will come jumpstart me tomorrow. My questions for the forum are, Has anyone had this problem before with the battery apparently draining fully? Could the battery have completely drained by me leaving an internal light or something on in the car? ( I dont think I did). Is it even safe to jumpstart these cars? Ive not drive the car for a week or so in the past an havent had this issue. Im hoping it is just the battery and nothing more serious. But, will appreciate any feedback from anyone in s550 land who might can shed some light on this for me.

 

Have you tried charging the battery or load testing it? That's where I'd start. Keep in mind the battery just may be toast.

 

I can leave my 2015 (with original battery) for 3-weeks and it will still start.

Something is either wrong with the battery or something is sucking too much current while you are not using the car.

 

Ask your Mercedes tech friend tomorrow and let us know.

 

Thanks so much for all of the responses to this post. My Mercedes tech friend did drop by yesterday to see what was going on. He was able to start the car using a charging pack. All tests came back negative as far as alternator problems etc. So, it was apparently just a battery issue. I did have to leave the car running and drive it around for 30-45 mins to allow the battery to fully charge. Just tried it today and all seems well. In hindsight I think I might have accidentally left the start button engaged when I last exited the car. But he did recommend investing in a trickle charger since I do only drive this care once or twice a week.

 

I have similar driving habits, use the car twice a week. When I come home I immediately connect a charger. I good way to check the battery is to measure the internal impedance. Xentry will provide this value in the diagnostics. Another way check your car is to measure the quiescent current. This is the current drawn when the car is in sleep mode, which means everything is turned off all doors are closed. All systems are asleep. Not easy to do. The value should be about 50 mA.

 

Same situation with my 2022 S 580. These cars really want to be driven more frequently than I typically drive, there are a lot of monitoring/communication systems online continuously taxing the 12v battery. The Mercedes me app would throw a “low charging battery” after about one week and a “critical” warning after about 10 days.

Solution for me was indeed a trickle charger. I purchased this one from the dealer. At a premium I'm sure, but if I developed battery problems later I wanted to be able to demonstrate that I’d followed my dealers instructions.

This is what the dealer provided: