Dying Battery?
Thread Starter
Senior Member
Joined: Mar 2010
Posts: 477
Likes: 124
2016 S550
Dying Battery?
Weird thing happened today, the car cranked a few cranks but didn't start. After that, it struggled and had the symptoms of a dead battery. This was just after I returned from a 2 hour drive. It seems to be a dead battery, as a jump start started the car right away.
However, what is weird now is that when I open the driver door from inside, after parking the car, the other doors do not automatically unlock. I would have to press the unlock button on the door. Does this seem to be caused by the low/weak battery? Or are they not related? Perhaps some module that controls all that is bad..and running my battery down while it is parked? I had zero signs of a bad battery until it randomly did not start. Seemed like I left something on, but nothing is left on! Drove 2 hours, parked it for a few hours. Came back and got a weak crank then no cranks.
However, what is weird now is that when I open the driver door from inside, after parking the car, the other doors do not automatically unlock. I would have to press the unlock button on the door. Does this seem to be caused by the low/weak battery? Or are they not related? Perhaps some module that controls all that is bad..and running my battery down while it is parked? I had zero signs of a bad battery until it randomly did not start. Seemed like I left something on, but nothing is left on! Drove 2 hours, parked it for a few hours. Came back and got a weak crank then no cranks.
Junior Member
Joined: Aug 2010
Posts: 47
Likes: 5
2008 C300
Dying battery?
My 2008 C300 had very infrequent problems with remote control of the door lock/unlock. Dealer could not reproduce the problem. Both or my remotes and car battery checked OK. Still it Appeared to be battery related: I learned that when the problem appeared, connecting a charger tor just a second or two would clear the problem. Replaced the battery; didn’t help. This went on for a couple of years until I got an intermittent charging system fault message while on a road trip. Went to the local Mercedes dealer, who could not reproduce the charging system fault and sent me on my way. Out of desperation and fear of being stranded on the highway, I had the alternator replaced at an Indy shop. That was a year ago, and I have experienced no more charging system faults nor door lock/ unlock problems. Not certain what was at fault, but the problems are gone.
Super Member
Joined: Sep 2015
Posts: 848
Likes: 87
From: Milwaukee, WI USA
2012 C300 4Matic
The thing about cars today is they are so sensitive when it come to electronics that it is not unusual for the battery to go bad with no warning. If the car doesn't sense the right voltage, the car won't start. If the battery is original, not a bad idea just to change it. Best way would be to load test it. Start there and see what you get.
As for your doors now not automatically locking it could be the battery was low enough it lost that memory feature and they need to be reset.
Good luck. Hope it is a simple fix.
As for your doors now not automatically locking it could be the battery was low enough it lost that memory feature and they need to be reset.
Good luck. Hope it is a simple fix.
Super Member
Joined: Nov 2008
Posts: 604
Likes: 29
From: SA
2008 C350-Sport-AMG-Active Agility Pack(Not reliable) +Izuzu KB6 3L(It seems Reliable)+Mazda
Batteries:How quickly does the voltage drop after a charge is removed or car switched off, my weird experience years ago.
My uncle from a remote location asked me if I could build him a 12V generator cheap to charge 2 new batteries for whatching TV(No solar).
I went along got a 5HP Honda engine, used a 12V VW-Beatle alternator, made stand etc. I decided to fit an automatic electronic cutoff device, so when the battery at charge reached 14.7V, the engine is cut. Long story short I used my battery to calibrate the system, worked fine.
I then go out and bought two new batteries locally from a dealer. Then my problems start, as they both seperately reached 14.7 volt the engine is cut, but just before it dies it starts again and process repeated. After 2 days of headscratching I proved both batteries to be possibly problematic.(They were fully charged by me for 24 hours before used).
Arriving at the dealer both batteries failed heavy load test just. He gave me two other batteries, TOK, my problem solved.
Some sort of a lesson learned about batteries.
My uncle from a remote location asked me if I could build him a 12V generator cheap to charge 2 new batteries for whatching TV(No solar).
I went along got a 5HP Honda engine, used a 12V VW-Beatle alternator, made stand etc. I decided to fit an automatic electronic cutoff device, so when the battery at charge reached 14.7V, the engine is cut. Long story short I used my battery to calibrate the system, worked fine.
I then go out and bought two new batteries locally from a dealer. Then my problems start, as they both seperately reached 14.7 volt the engine is cut, but just before it dies it starts again and process repeated. After 2 days of headscratching I proved both batteries to be possibly problematic.(They were fully charged by me for 24 hours before used).
Arriving at the dealer both batteries failed heavy load test just. He gave me two other batteries, TOK, my problem solved.
Some sort of a lesson learned about batteries.
Last edited by Moto_Guzzi; Aug 29, 2018 at 12:30 PM.
Thread Starter
Senior Member
Joined: Mar 2010
Posts: 477
Likes: 124
2016 S550
I will replace the battery today and hopefully that fixes the door unlock feature. Not sure if it’s a memory issue since the car is on and running while I set the settings in vehicle settings by enabling and enabling each setting.
I would also have to check the alternator since it may not be charging the battery..I will know if the new battery also dies soon.
The current battery is a factory battery replaced under warranty about 4 years ago.
I would also have to check the alternator since it may not be charging the battery..I will know if the new battery also dies soon.
The current battery is a factory battery replaced under warranty about 4 years ago.
Super Member
Joined: Nov 2008
Posts: 604
Likes: 29
From: SA
2008 C350-Sport-AMG-Active Agility Pack(Not reliable) +Izuzu KB6 3L(It seems Reliable)+Mazda
My 2008 C300 had very infrequent problems with remote control of the door lock/unlock. Dealer could not reproduce the problem. Both or my remotes and car battery checked OK. Still it Appeared to be battery related: I learned that when the problem appeared, connecting a charger tor just a second or two would clear the problem. Replaced the battery; didn’t help. This went on for a couple of years until I got an intermittent charging system fault message while on a road trip. Went to the local Mercedes dealer, who could not reproduce the charging system fault and sent me on my way. Out of desperation and fear of being stranded on the highway, I had the alternator replaced at an Indy shop. That was a year ago, and I have experienced no more charging system faults nor door lock/ unlock problems. Not certain what was at fault, but the problems are gone.
I think your experience is also important to take note of. The alternator is indeed major part of a cars electrical power system. To measure these fluctuations/spikes may be a problem, IE detecting them in advance.
Wirering(Bad connections/intermittant contacts)---Components(seen fail with temperature changes)---Battery-Alternator---Drive Belts.
Your problem comes when fault symptoms are not caused by straight forward faults.
Your problem comes when fault symptoms are not caused by straight forward faults.
Last edited by Moto_Guzzi; Aug 30, 2018 at 01:48 AM.
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Thread Starter
Senior Member
Joined: Mar 2010
Posts: 477
Likes: 124
2016 S550
Changes the battery out with a Walmart Everstart H7 battery that comes with a 5 year warranty.
The battery I had replaced was a genuine battery from 06/14 according to the label. It barely made it past 4 years... currently dropped it off to a auto parts store to charge it up and do an deep test.
Also had them test my alternator and said everything passed, with the Walmart battery.
So far so good. The weird door lock issue went away.
The battery I had replaced was a genuine battery from 06/14 according to the label. It barely made it past 4 years... currently dropped it off to a auto parts store to charge it up and do an deep test.
Also had them test my alternator and said everything passed, with the Walmart battery.
So far so good. The weird door lock issue went away.
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Super Member
Joined: Nov 2008
Posts: 604
Likes: 29
From: SA
2008 C350-Sport-AMG-Active Agility Pack(Not reliable) +Izuzu KB6 3L(It seems Reliable)+Mazda
A borderline battery=Instability=Confusion, my experience, and not just in cars, big batteries(15-20 year lifespans) not more able to smooth out poor AC fed to rectifiers-batteries-electronic systems..
