[alopolo]

My 12v battery was replaced last year for the second time since purchase after my start stop functionality stopped working and my mercedes me app was displaying a partially charged battery error. I also had difficulty using remote start. Since the replacement all issues went away but now it's back again. I'm so shocked how poor the quality on these batteries are and why they need replacement so often. Anyone else has issues with these batteries?
2019 a250

 

[veeeight]

It’s not so much that the batteries are rubbish, they aren’t, but this is a problem that affects all EU6 cars.

The alternators do not charge the batteries to 100% any longer like in the good old days, instead relying on your driving pattern to charge the remaining 20%. Or an external charger if you don’t use the car much.

If your driving doesn’t fit the prescribed pattern, it won’t charge the remaining 20%.


See post #6 in this thread.

 

[alopolo]

It’s not so much that the batteries are rubbish, they aren’t, but this is a problem that affects all EU6 cars.















The alternators do not charge the batteries to 100% any longer like in the good old days, instead relying on your driving pattern to charge the remaining 20%. Or an external charger if you don’t use the car much.















If your driving doesn’t fit the prescribed pattern, it won’t charge the remaining 20%.























See post #6 in this thread.

Interesting my dealership never told me this and I never had a problem with my bmw such as this. The dealership just replaces my battery every year, works fine for about 12 months then it will always be partially charged no matter how much highway driving I do.

 

[veeeight]

no matter how much highway driving I do.

Exactly this.
Highway driving is the worst scenario / least optimum scenario for charging that last 20%.

it’s only under braking and/or intensive over-run where that last 20% charging takes place.

 

[srea064]

Put the trip meter up on the dash area between the speedo and the rev counter. Move one option down to the first mpg gauge. When driving lift off the accelerator and let the car coast. You will see the mpg shoot up and the gauge also goes right into the green area. This means the last 20% is being charged.

With this gauge up on the motorway don’t just sit a a speed. Speed up then coast a little way. This will charge the battery up that last 20%.

Gauge I mean mean looks like this…

https://www.aclassclub.co.uk/cdn-cgi/image/format=auto,onerror=redirect,width=1920,height=1920,fit=scale-down/https://www.aclassclub.co.uk/attachments/20200228_175346-jpg.4834/

 

[alopolo]

I drive 80% city mostly stop and go flooring it here and there at the lights and on ramps. but the dealership told me to drive more conservatively with coasting on the highway to charge the battery. However none of this worked. I'm just waiting for my annual battery replacement next week :\

 

[PaulH]

When driving lift off the accelerator and let the car coast. You will see the mpg shoot up and the gauge also goes right into the green area. This means the last 20% is being charged.

Mine regularly swings round to the 'Charge' zone but the voltage in MBUX never changes from 14.8v. I've read that reduced charging is at about 13v, I've not seen that on the cars display, but haven't yet got round to having an independent voltmeter in the car. The only time Auto Start/Stop has worked has been immediately after having it on a Ctek for two days shortly after getting the car with battery warnings, and secondly after a 200-mile round trip a couple of weeks later. In between those two and since the use is generally local with accelerating and braking, with Stop/Start showing as disabled (as opposed to switched off), so that seems to go against the 'long trips are bad for full charging' and 'braking and over-run are needed'.

It seems to me that once the battery has become fully charged on a long run, the voltage and hence current and load (miniscule) on the alternator hence engine can be reduced. Anything else would seem to be to be 'dumb' charging and not at all 'smart'. I've also read that under acceleration the charge can be reduced to give you that extra fraction of a horse-power!

 

[veeeight]

so that seems to go against the 'long trips are bad for full charging' and 'braking and over-run are needed'.

See page 5&6 of this pdf.

I hope to see your experiments charted and reproduced on here too

https://www.ablemail.co.uk/sites/default/files/products/ablemailbatterychargerselectionguide.pdf

https://www.12voltplanet.co.uk/user/downloads/Smart%20alternators%20&%20regenerative%20braking%20info.pdf

^ On that second pdf, the last part of the journey is motorway miles, and you can see that the spikes to 14.8V are much more infrequent than the earlier part of the journey.



If you are going to connect a volt meter to log charging voltages - you need to be on the actual battery terminals itself. Anything downstream of that and you'll be going through the battery management and monitoring sensor, which is part of the negative lead connecting the battery to the body.

 

[PaulH]

Correct, but I'm going to monitor the system voltage first. Both of those links seem to refer to additional equipment with even the spikes in the second one less than the voltage that is shown on MBUX, and to see spikes an oscilloscope would be needed.

But my point that long steady motorway runs DOES charge the battery enough to prevent the battery warning still holds, regardless of what accelerating and decelerating does. No warnings this morning after an hours mostly steady running yesterday. I've seen comments that the cars need to be driven more, which makes a nonsense of 'smart' charging reducing emissions. Ctek make a range of chargers including one specially designed for vehicles with stop/start, and a comment that it may need to be used once a month. Ridiculous, daily driver cars never needed that for decades before all this fancy crap came in. But this seems to be an MB issue, the previous Golf 7 never gave any battery warnings and stop/start worked for the two years I had it with less use than the MB is getting at the moment.

 

[veeeight]

I've seen comments that the cars need to be driven more, which makes a nonsense of 'smart' charging reducing emissions. Ctek make a range of chargers including one specially designed for vehicles with stop/start, and a comment that it may need to be used once a month. Ridiculous, daily driver cars never needed that for decades before all this fancy crap came in

Yep. There are scores of posts on here and across social media regarding batteries on the W177 not being in a sufficient state of charge over time.

Lockdown exacerbated the shortcomings of the system.

 

[alopolo]

Dropped the car at the dealership today, they confirmed they will replace the battery again under warranty after 12 months. My battery voltage is almost always high 14s. Just as a comparison my BMW 330i hasn't had its agm battery replaced since 2017 and it works great. Start and stop functions normally too.

 

[veeeight]

Just a general caveat about using battery voltage solely as a health indicator.

Voltage on its own doesn't tell the full story, the SOH must be measured separately using a different instrument to a voltmeter.

I've measured battery voltage before now, where it shows a healthy 13.2V, but its SOH has been less than 50%.

What are SOC and SOH of a battery, how to measure them?

Battery SoC/State of Charge describes the remaining electricity available in the cell. SoH is the difference between used/fresh batteries.

www.biologic.net

 

[PaulH]

In the olden days they put a low resistance, high wattage resistance like a heating element across the battery posts with a voltmeter between the posts as well and noted how quickly the voltage fell. Haven't seen one of those for a very long time.

 

[srea064]

@PaulH I remember those. Back in the day I used to work for GKN Autoparts, later Partco Autoparts and we used them all the time. They used to give an indication of how well the battery performed under load.

 

[Skhm28]

Hi, My battery is constantly showing partially charged. I sprang for a Ctek MXS 5.0 and hooked it up this morning to see if things improve.

Question I have is, will MB replac e under wty if this doesnt improve? I have four months left before the three years are up, so is it worth a call or will they consider battery non wty item?

I have CTEK set to Car AGM mode, and lights 1,2,3 are on after an hour - do I leave it to get to light 7 ?

thanks for any response.

 

[veeeight]

Question I have is, will MB replac e under wty if this doesnt improve? I have four months left before the three years are up, so is it worth a call or will they consider battery non wty item?

Depends how charitable the service/warranty manager feels on the day. If you go in with a genuine fault/complaint eg: "My Start/Stop doesn't work at all" - they may run battery tests on your poorly performing battery, and determine that its SOH is below par, and replace it under warranty.

If on the other hand, you've fully charged it yourself with a ctek, and your S/S is now working.... you haven't got a fault to report....

 

[veeeight]

I have CTEK set to Car AGM mode, and lights 1,2,3 are on after an hour - do I leave it to get to light 7 ?

At least 6 before it's "fully" charged.

 

[srea064]

My car is now in an extended warranty period, so the initial 3 year has expired. I still had my battery replaced under warranty 👍

 

[Forrester]

My car is now in an extended warranty period, so the initial 3 year has expired. I still had my battery replaced under warranty 👍

I’m guessing your extended warranty is more prescriptive than the laissez faire approach of the MB warranty where it depends on the luck of the day.

 

[Skhm28]

Depends how charitable the service/warranty manager feels on the day. If you go in with a genuine fault/complaint eg: "My Start/Stop doesn't work at all" - they may run battery tests on your poorly performing battery, and determine that its SOH is below par, and replace it under warranty.

If on the other hand, you've fully charged it yourself with a ctek, and your S/S is now working.... you haven't got a fault to report....

Thanks for the insight. I'll leave it charging now till 6 or 7 - and see if the partial charged alert goes. If not ill leave it a week and report to MB to see if they can test it and REPLACE it.
I switch off SS as I hate it, but will see if it works or not.

thanks.