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I got a notification from my app this morning that my starter battery was critical. The car was at a detail shop and they had apparently left it unlocked all night. Which raises a couple questions for me:
1. I've heard, but never until now confirmed, that leaving the car unlocked will drain the starter battery. Is there any reason for this? Any way to fix it? I park my car in my garage every night. I lock it because I was told about this issue, but I'd really rather not. Why is this necessary?
2. After driving my car for a couple hours, the app now tells me that the starter battery is "partially charged". I'm about to leave for a trip in Canada, where the car will be parked outside in the cold for 8 days without starting (nor any way for me to start it). I've never worried about this with other cars that I've taken on this trip, but this weird starter battery behavior has me worried. My car is about a year and 11,000 miles old; should I be replacing the battery before this trip? Or assuming I lock the car (which I obviously will) should it be OK?
Never really worried about the battery on any car except my quirky Lotus... I'm a little surprised that you've got to worry about it on a $130,000 super-wagon!
I keep my cars unlocked in garage for weeks at a time and no issue. Probably during the detailing the doors were open, interior lights on, and/or infotainment on, that'll drain the battery, or they forgot it turn it off.
Last time I got a critical notification (car was new and I was messing around with MBUX while the car was off), the battery voltage was over 12.2V, which is still over 50% battery capacity for an AGM battery.
My car sits in the bat cave unlocked all the time. It's never been a problem leaving it that way over night. The only time there has been an issue with the battery is when I haven't driven the car for a month or two, which happens more often now that I'm working from home due to CV-19.
Now I usually throw on the trickle charger if it gets past a week or two without starting it just so the battery doesn't get too deeply discharged.
Before you leave for the trip, have it trickle charge fully. It will take as much as 12hrs+. You should practice of having it trickle charge the battery once a month, if possible. Once you have it fully charged, I believe you should be fine.
I also parked my car inside of garage unlocked and I have not experienced this kinds of rapid battery draw over a period of 8-12 hrs.
I just replaced my battery after 3.5 yrs of ownership of the car after having so many electronic gremlins popped up in many instances.
Whether having a car locked or unlocked should not really make such a drastic draw on battery, I really think your issue is too many short and infrequent short trips, thus your battery did not have a good chance of recharging.
Thanks all. This is useful input. It may be, as suggested, that the detailer left the doors open (what a weird oversight though!).
I do think that I've left my car unlocked for a couple days in the past and not had this happen. But at the same time the seller told me to be sure I always locked the doors or this could happen.
Before your trip and before you charge it, take it to the dealer and tell them you’re having problems, ask them to test the battery and replace if necessary. I’d get a good smart charger, like a CTEK MXS 5.0 if you don’t have one as well. Plug it in once a month or so and whenever it will sit more than a week, not hard.
I had left my car locked in the garage for 3 weeks and when I came back it was dead... plus it was snugged up against my tool cabinet where I keep my charger!!!
Needless to say, I learned how to unlock the car with the key (you have to remove the cover over the door handle) and used a jumper to start the beast. The car is a 2018 with 30K on her... she gets a lot of city driving with a mix of 250 mile weekend driving every 3 weeks.
The reality is that these batteries are really only good for about 3 years. So maybe it's time for you to change your battery... no need to stick with OEM on the battery as you can do find with a high end autozone battery. I put an "interstate" in mine. Just make sure it is the highest amp or cranking power that will fit in the footspace of the OEM. Figure $200 or so... don't buy the cheapest as that will be a mistake.
the idea that leaving the car unlocked runs down the battery more is crap. No matter what the deal is the car has stuff running all the time.. (keyless go for example) and of course the alarm.
We had the same issue the day before a trip and it turned out that the battery was bad after less than 2 years. Get to the dealer and have they can test it. I certainly would not want to take a trip when the battery is suspect.
A lot of modern cars seem to have very parasitic electrical systems. This problem is far from isolated to our vehicles. I've been helping my Dad diagnose his 2020 Porsche 992 C4S Cab that has a lithium battery. We keep finding it dead as a doornail at seemingly random times, shortly after having been driven for instance. He has had trouble keeping the silly factory charging system (cigarette socket in passenger footwell) maintaining the battery properly as well. It just happened again and I told him to tell the dealer to just replace the stupid battery, they agreed.
It's not an issue. These cars maintain a data connection while parked, so there is some battery drain. If you parked it for extended period you can activate the Standby mode, which will turn all of that off until you start it next time. I've gotten critical battery alerts before as well while my C63 was in service for a few days and they were working on it, and I've gotten them while my PPF was being put on, too. I now trickle charge before I take the car in and it hasn't happened since. It takes a while for the battery to fully charge in these cars, so you have to go on a long drive or put it on a trickle charger. BTW, I also park it in the garage unlocked and these days mostly drive it on weekends only. Partially charged just means less than 100%, but you don't actually know what the charge level is. If it doesn't go to Charged after a drive, then you just have to drive more. Your trip will fully charge it.
As others have noted, this behavior is alarming but normal. I received the same warnings when my car was in a detail shop and even when I am working on the car in my own garage. Each time you open a door, MBUX and other electronic systems turn on in preparation for engine start. Even when you close the door and walk away, the systems remain active for a period of time, using battery power (the systems may shut down earlier if you lock the car). As detailers or others open and close doors during service work, the electronic systems are effectively running continuously, leading to the starter battery warnings. The battery has never been drained to the extent that I am unable to start my car. A drive of 30 minutes seems to restore the battery to full charge. I have left the car locked and untouched for as long as five weeks without any battery warnings or issues.
It's also a bit of a case of TMI. I'm willing to bet that past cars often had partially charged batteries or even low batteries, but they didn't send a notification to one's phone or had a companion app where somebody with OCD can continuously check the battery status.
Of course it can be a real battery issue, but it is a known "bug", where the ME App gives this error, but also in the car the dash then displays the same message. You can start and drive, etc. and nothing wrong. In my previous (pre facelift) car I had it few times, also few minutes after a trip.......so no reason that the battery should be critical.
There is a service bulletin for this IIRC, but don't have it here.
I just brought my car in for the first service and I mentioned that I keep getting critical battery warnings. They tested it and it failed, so they replaced it under warranty. I've never seen a battery fail so fast, but at least it was covered.
I just brought my car in for the first service and I mentioned that I keep getting critical battery warnings. They tested it and it failed, so they replaced it under warranty. I've never seen a battery fail so fast, but at least it was covered.
You wanna try to figure what is causing your battery to go bad. Is it normal or abnormal...
> Is the car under driven (less than once every 2 weeks)
or
> Is the car driven frequently but keeps discharging the battery or not charging it well.
Last edited by CaliBenzDriver; Jan 31, 2022 at 11:37 PM.
^Good things to consider and to add to the last point, is the vehicle driven frequently for short trips and/or constantly started in low temperatures that leads to the discharging of the battery and not allowing enough time for it to be charged again.
There's definitely something wrong here. Either the factory batteries aren't that great and/or these cars have very parasitic electrical systems. I'm leaning towards the latter but it's hard to tell for sure without controlled testing. What I do know is that I've had several other cars that I've driven in a similar fashion and have never had issues anywhere near to this degree/frequency. Multiple threads/posts now, clearly not an isolated issue or necessarily behavior-related.
You can display the battery Voltage & Current while driving through MBUX.
This will effectively show you if computers glitches are causing the ALTERNATOR to DRAIN batteries below 12Volts instead of charging it between 12.6V /14.9V.
You can display the battery Voltage & Current while driving through MBUX.
This will effectively show you if computers glitches are causing the ALTERNATOR to DRAIN batteries below 12Volts instead of charging it between 12.6V /14.9V.
Good idea but unfortunately I don't think that voltage is available for an AMG, perhaps it was replaced by transmission temperature?
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