2019 C300 Battery Charging Issues

[356speedster]

Evening all..... Is anyone else having issues charging their batteries on their late W205 cars?

We have a pair of 2019 205 series cars, my C63S coupe and my wife's C300 cabrio. Neither car is doing (m)any miles at the moment, so I'm having to resort to a battery charger. I have a brand new Ctek MXS 5.0 and for my AMG, this is working just fine. In about 36hrs from receiving the MercedesMe low battery warning, the MXS full recharges the battery. Perfect. However, the same cannot be said for the C300...

For some reason the C300 just will not charge. The MXS is connected to both cars, as per the owners hand book (red underbonnet terminal & ground connection just behind the headlight, on the chassis). When connected to the C300, the MXS lights up as per the AMG and indicates it's charging. Sadly, it never gets anywhere and the lights don't go up the scale. The MXS has 8 charge stage lights, but it never gets past stage 2 on the C300 and the charger gets a lot hotter than when charging the AMG.

I'm stumped. Has anyone else experienced this with a (mid) 2019 C300 or similar aged car? If we drive the car, it charges itself absolutely fine and after a good drive, it will sit on the drive untouched, happily for 3weeks before alerting for a flat battery via MercedesMe. Puzzled, thanks for your thoughts.

 

[barian]

This does seem very odd. The fact that it charges one of the cars successfully would suggest that the charger is not faulty. However 36 hours does seem a long time - I think something around 12 hours would be more normal. Does it really take that long, or perhaps are you leaving it that length of time before checking? If the charger is getting hot with the C300 it suggests that power is going somewhere and I wonder if there is maybe a high resistance somewhere. Assuming you are getting a good connection on the battery terminal and ground points, the only thing I can think of would be to try a different ground point on the chassis or engine block. But I would be inclined to ask your dealer to look in to the problem, especially as the car will still be in warranty. One final thought is that I am fairly sure your cars will have AGM batteries and you should be using the AGM setting on the CTEK, although I don't think this would be the explanation if you are not. Apologies if I am teaching you to suck eggs.

 

[Jigglyjohnson]

Is the c300 a new eq model with a 48v battery system as if it is you would actually be charging both the 12v and the 48v battery.

 

[356speedster]

Is the c300 a new eq model with a 48v battery system as if it is you would actually be charging both the 12v and the 48v battery.

It's not no, "normal" C300, I bought it specifically as I didn't want an EQ

This does seem very odd. The fact that it charges one of the cars successfully would suggest that the charger is not faulty. However 36 hours does seem a long time - I think something around 12 hours would be more normal. Does it really take that long, or perhaps are you leaving it that length of time before checking? If the charger is getting hot with the C300 it suggests that power is going somewhere and I wonder if there is maybe a high resistance somewhere. Assuming you are getting a good connection on the battery terminal and ground points, the only thing I can think of would be to try a different ground point on the chassis or engine block. But I would be inclined to ask your dealer to look in to the problem, especially as the car will still be in warranty. One final thought is that I am fairly sure your cars will have AGM batteries and you should be using the AGM setting on the CTEK, although I don't think this would be the explanation if you are not. Apologies if I am teaching you to suck eggs.

Thanks Barian...... The AMG takes somewhere between 24-36 hrs, I don't check it regularly to know exactly how much time it takes. The Ctek also charges my Ultima's battery happily, so as you say, it's not a charger issue. I'm connecting both cars in exactly the same way, both using AGM mode, but I have also tried some different ground points on the C300, but the result is still the same - a hot charger and not progress. It's really odd.

As you say it's in warranty (and booked in for it's 2nd service at the end of the mth), so worst case scenario they'll have to check it out in the workshop, but I wanted to see if anyone here has experienced anything similar.....

 

[rf065]

The Ctek should tell you if a battery cannot be charged. It shows a fault code and stops trying to charge.

 

[356speedster]

The Ctek should tell you if a battery cannot be charged. It shows a fault code and stops trying to charge.

Nope, it just keeps trying and gets hot

 

[190]

Bring back chargers with an ammeter so you can see what's going on.

The symptoms suggest there is something running the battery down. If the charger is getting hot then it's producing a charging current which should eventually fully charge the battery. The charging current would then fall off and the charger would get cooler. For it never to reach that stage means something is running the battery down almost as fast as it is being charged.

If the charger is removed how long does it take for the battery to go flat. Edit: you already said 3 weeks. I don't think a newish car should flatten it's battery in 3 weeks. Typically the alarm current draws 3-5 Ah per week which would not get anywhere near to fully flattening the battery in 3 weeks. Perhaps the alert senses an only partially discharged battery. I still think something is drawing a higher current than it should. Cars sometimes don't going to sleep properly and continuing to draw more current than they should.

 

[356speedster]

I don’t think anything is pulling the battery down to counteract the charging, unless it’s doing something odd that it doesn’t do normally. The reason I say this, is that both cars only survive 2.5-3 weeks before they complain that they need juice, so they’re in sync here, yet one of them charges quite happily. It’s very peculiar.

When the AMG complained for its second time (last year, it was used less than the cab) that the battery was flat after 3wks, I called the dealer and they said it’s normal as there’s a lot of monitoring electrics in these cars. They did take it in and ran diagnostic, but concluded no issue. On balance I think they both discharge at the same rate, but I can’t for the life of me figure out why one car just won’t charge!

 

[Trevorlm47]

Evening all..... Is anyone else having issues charging their batteries on their late W205 cars?

We have a pair of 2019 205 series cars, my C63S coupe and my wife's C300 cabrio. Neither car is doing (m)any miles at the moment, so I'm having to resort to a battery charger. I have a brand new Ctek MXS 5.0 and for my AMG, this is working just fine. In about 36hrs from receiving the MercedesMe low battery warning, the MXS full recharges the battery. Perfect. However, the same cannot be said for the C300...

For some reason the C300 just will not charge. The MXS is connected to both cars, as per the owners hand book (red underbonnet terminal & ground connection just behind the headlight, on the chassis). When connected to the C300, the MXS lights up as per the AMG and indicates it's charging. Sadly, it never gets anywhere and the lights don't go up the scale. The MXS has 8 charge stage lights, but it never gets past stage 2 on the C300 and the charger gets a lot hotter than when charging the AMG.

I'm stumped. Has anyone else experienced this with a (mid) 2019 C300 or similar aged car? If we drive the car, it charges itself absolutely fine and after a good drive, it will sit on the drive untouched, happily for 3weeks before alerting for a flat battery via MercedesMe. Puzzled, thanks for your thoughts.

Hi
I also have a 2019 C300 Cabriolet and I’m getting some weird battery charging symptoms. What with lockdown and winter the Stop-Start died back last November, then this March the 12 volt battery warning appeared followed by the alarm going off intermittently. However the car always started and ran well. The web suggested the alarm problem was due to the battery. Short runs in the car (lockdown rules) fixed the problem for a day at most before they all returned
I bought a CTEK MXS-5 and connected it up. I selected the Car AGM option and waited. The display built up to Stage 3 then appeared to stall. After 18 hours it had reached 4, but there it stopped. I left it another 18 hours but the display dropped back to 3 and stuck there. A multimeter tells me that while running at stage 3 the battery voltage rises to 12.8 volts then suddenly drops to 12.5v, then builds back up to 12.8v. It loops like that ad nauseum. The CTEK gets warm, but not what I would call hot, the display has never risen above stage 4.
The car runs well, and Stop-Start works again. Puzzled, but a gift horse is a gift horse!
I will query this at my 2nd service in 60 days.
This isn’t much help to you, but you are not alone.

 

[356speedster]

Hi
I also have a 2019 C300 Cabriolet and I’m getting some weird battery charging symptoms. What with lockdown and winter the Stop-Start died back last November, then this March the 12 volt battery warning appeared followed by the alarm going off intermittently. However the car always started and ran well. The web suggested the alarm problem was due to the battery. Short runs in the car (lockdown rules) fixed the problem for a day at most before they all returned
I bought a CTEK MXS-5 and connected it up. I selected the Car AGM option and waited. The display built up to Stage 3 then appeared to stall. After 18 hours it had reached 4, but there it stopped. I left it another 18 hours but the display dropped back to 3 and stuck there. A multimeter tells me that while running at stage 3 the battery voltage rises to 12.8 volts then suddenly drops to 12.5v, then builds back up to 12.8v. It loops like that ad nauseum. The CTEK gets warm, but not what I would call hot, the display has never risen above stage 4.
The car runs well, and Stop-Start works again. Puzzled, but a gift horse is a gift horse!
I will query this at my 2nd service in 60 days.
This isn’t much help to you, but you are not alone.

Very similar symptoms, although ours hasn't gone as far as triggering the alam...... We did have the mirrors refusing to fold when locked and then the external light delays stopped working, but both issues have self-healed in the last week! The car was used on a 50min out & 45min return journey on Friday, which still only have the battery being reported as "Partially Charged" in the app (Stop-Start isn't working still).

We'll try to use it as much as we can, but the service isn't due for a couple of mths, so unless it plays up further, it'll be a while before it gets to the dealership. I'd be interested to hear how you get on at your dealer when your car is serviced, if you wouldn't mind giving feedback. Thanks!