I have a 14 E350 with 46000 miles I got the warning for a bad auxiliary battery replaced it however my stop and go is not functioning correctly. I checked my 7 year old battery on the hidden menu and it shows UB 11.7 after starting it and while driving it goes to 14.5 to 14.8 after driving and stopping for a while it drops back down to 11.9 to 11.7. I stopped at advance auto and had them check it the guy I wasn't quite comfortable with tell me it wasn't the battery but the alternator. I have a hard time believing that since everything else I have researched tells me its the battery. I am headed to get a battery now what are your thoughts?????

 

Concur. The 14+ during operation shows the alternator to be working just fine. The 11.7 is a dead battery. Proceed with your plan.

 

Completely agree, Battery.

 

You need a Main Battery for sure. Seven years on the previous is great, and almost unheard of in these cars.

BTW, ECO Stop/Start works off the main battery, not the AUX. When it's not working in my 2016, that's my clue to recharge the main battery.

 

I'm wondering if everything is actually fine. You're going to get lower battery voltage when the temperature is low. Same with the start/stop, takes a while to kick in especially if it's cold. On my 2008, I have the original AGM battery at 13 years and my W212 has the original 10 year old battery. If you don't trust the load test at Advance Auto, you can go to Autozone and get another load test. You could also get the car scanned to see if there are any other MB specific error codes or maybe clear any existing ones.

 

Just got back I got the battery from AutoZone the AGM H8 the ride seems smoother the battery is now registering 12.4 it is still in the high 14.4-8 while driving. The stop start has not reset yet I turned it off for now I plan to have it serviced at Buckhead if I can there in time. I am headed off to the store again so I will check it out again I do feel much better than earlier. Thank you for the follow-up I will keep you posted.

 

Yes, my batteries in my '90's and 00's lasted a long time as well, unfortunately they did not have a charging system that was designed not to charge the batteries fully, they say over 1-2 mpg. just stupid. my '12 212 made it seven years, but it has 30k miles and was on a trickle charger winters. my '13 had the battery replaced last fall so six years.

 

We bought our E350 from Buckhead.. yuck.

They replaced our main battery a few days after we took delivery due to stop/start not working. So yes, main battery is the culprit.

Don’t worry over the voltages you see. Ours also charges at 14.8 or so. Our Macan’s battery was also just replaced and it at times will charge at 15V. It required registering the new battery and I have yet to see a straight answer as to whether batteries have to be registered to the facelift W212s. But I will say that stop/start worked immediately after our battery was replaced at the dealer. That yours still isn’t working is weird.

 

I replaced it myself I haven't made it to the Dealership yet I am stationed in South Carolina at the moment just waiting to head that way. Would you know if Tony is still in Services? He was always straight forward and honest with me.

 

Everything is back to normal the start stop just started working again I am a happy camper, I think? Thanks to the push in the right direction

 

Thanks for letting us know. Nice job!

 

And thank you for your service! Semper Fi

 

Couldn’t tell you. The salesperson was such an arrogant asshat that we will never go back. Only went back that one time because of the “We Owe” sheet.