Strange battery charging issue
Thread Starter
Senior Member
Joined: Jul 2011
Posts: 328
Likes: 56
2012 S350 Bluetec 4MATIC; 2011 ML350; 2005 C230k;
Strange battery charging issue
I need help/advice.
Yesterday I replaced main battery on my 2012 W221. If the engine is in idle or if it accelerating the battery is not charging. But once I stop accelerating the battery start charging. Please see link below with video.
I did alternator test with DAS and it passed. During the test the battery was charging but once the test was done the battery stop charging even if I increased RPM. It looks like something is telling alternator when it has to start to charge battery.
Another observation:
When the vehicle is in park position after driving, the battery is discharging until I open the doors. Once I open the doors the battery start charging and it will charge until the vehicle start moving again. As soon as vehicle start moving the battery start discharging until I open the doors...
Here is second video below to better understand.
Any suggestion what can be wrong? What module is telling alternator to start charging? Can I trigger the charging circuit with DAS?
I don't have any errors. I'm expecting to see around 14V when the engine is running and charging state instead of discharging. Unfortunately I did not do same test with old battery so I don't know how the behavior was before I replaced the battery.
Yesterday I replaced main battery on my 2012 W221. If the engine is in idle or if it accelerating the battery is not charging. But once I stop accelerating the battery start charging. Please see link below with video.
Another observation:
When the vehicle is in park position after driving, the battery is discharging until I open the doors. Once I open the doors the battery start charging and it will charge until the vehicle start moving again. As soon as vehicle start moving the battery start discharging until I open the doors...
Here is second video below to better understand.
I don't have any errors. I'm expecting to see around 14V when the engine is running and charging state instead of discharging. Unfortunately I did not do same test with old battery so I don't know how the behavior was before I replaced the battery.
Super Member
Joined: Feb 2007
Posts: 613
Likes: 294
From: Republic of Texas
W203 W212 W211 R53MCS
Are you having any issues with the battery discharging?? or any messages displayed? Some of this new Intelligent Battery systems will reduce the charging voltage depending on the state of the battery. If you have a brand new battery, the voltage and state of charge is almost full.
Thread Starter
Senior Member
Joined: Jul 2011
Posts: 328
Likes: 56
2012 S350 Bluetec 4MATIC; 2011 ML350; 2005 C230k;
I did some searching and it looks like this behavior is normal. Here is what I found on daimler website:
"Each time the car is braked, kinetic energy is converted into heat and therefore goes to waste. This is why the E-Class incorporates efficient alternator management. This means that, whenever the engine is coasting and whenever the vehicle is braked, the voltage level in the vehicle electrical system is increased and the battery is charged. This increased alternator load assists the driver with braking and also helps to recuperate part of the braking energy, which is converted into electrical energy. This is why the experts refer to recuperation. Conversely, the alternator switches to no-load operation in certain situations – for example when accelerating or when the battery charge level is high – thus relieving the strain on the drive system. This process saves fuel to the tune of around 0.1 litres per 100 kilometres on paper (NEDC) and up to 0.2 litres per 100 kilometres when on the road in city traffic, where coasting and braking are more frequent than in the NEDC test cycle."
"Each time the car is braked, kinetic energy is converted into heat and therefore goes to waste. This is why the E-Class incorporates efficient alternator management. This means that, whenever the engine is coasting and whenever the vehicle is braked, the voltage level in the vehicle electrical system is increased and the battery is charged. This increased alternator load assists the driver with braking and also helps to recuperate part of the braking energy, which is converted into electrical energy. This is why the experts refer to recuperation. Conversely, the alternator switches to no-load operation in certain situations – for example when accelerating or when the battery charge level is high – thus relieving the strain on the drive system. This process saves fuel to the tune of around 0.1 litres per 100 kilometres on paper (NEDC) and up to 0.2 litres per 100 kilometres when on the road in city traffic, where coasting and braking are more frequent than in the NEDC test cycle."
