Long Islander

I have a 2018 E400 that is now 5+ years old with 32k miles. The car is used most days and there have been no warning signs about a low battery. The battery is the original AGM battery. Should I start thinking about a replacement battery to avoid getting stranded?

ua549

I also have an '18 E300 delivered in July 2017 that had the battery replaced in December 2021 at 4½ years. I got low battery warnings, but was never stranded. IIRC the car had 15k miles.

Long Islander

I haven't gotten any low battery warnings yet, so I guess I'll wait until I get them.

W205C43PFL

If it aint broken don't fix it : )

JTK44

I have a 2019 E450 that I picked up in December 2018. My battery is still going strong. I have 37,000 miles on it and drive it 5 to 7 days a week.

Both in the spring and the fall, I put a battery charger on it. So far so good!

kingscorpian27

I have a 2017, in it’s 7th year. Didn’t drive a lot when Covid started. Received the change battery notification a couple years ago and started to use a tricycle charger. If I play music for an extended period of time while the car is off I will receive the charge notification. Car is driven more frequently now so don’t receive message that frequently, just passed 35,000 miles a couple weeks ago.

2012 merc amg

Ive heard of the main batteries going for up to ten years the aux battery is another story and generally only good for 3 to 5 years if you're lucky.

The_Judge

I bought my 2018 E400 Coupe on November 3, 2017; it was brand new. The "on-board electrical system battery" was replaced on October 4, 2021, because the car would not start. At that time the car had only 11,412 miles on the clock (I stopped driving for business in March of 2020 due to the pandemic, and the lack of use may have had something to do with the battery's failure). To their credit, my Mercedes dealer did not charge me for the replacement of the battery or the associated labor.

ua549

You were still within the 48 month warranty period. Lucky you.
I was just out of the warranty period and it cost several hundred dollars for the replacement and labor.

W205C43PFL

Hmmm, how come you didn't just DIY it though, genuinely curious.

ua549

I'm not able to work on a vehicle due to my age (>80) and lack of equipment to diagnose problems. As with most things I'd rather pay others for the convenience.

W205C43PFL

Fully understand, good for you and please enjoy your vehicle in good health!

SpeedracerZ

I replaced the battery on my 2018 last fall. No warning lights but wanted to get it done before winter. You'll notice the start/stop stops working towards the end of the battery life. Replaced with a larger AC Delco battery from Advance Auto with no issues.

2012 merc amg

I think my main battery has had slightly lower voltage the past couple of years as the start/stop started working intermittently then and now never works so I've got a spare voltage regulator just incase but pretty sure it’s the main battery causing the issue but I don’t care though it’s nice to have the start/stop default to not working anyhow. The car is on a battery maintainer 6 months out of the year. I’ll just leave it as it is until it doesnt start who knows maybe get a few more years out of the main battery. Seems like these cars are very sensitive to looking for a high battery voltage to make the start/ stop functional.
I’ve had the battery tested twice at batteries plus and they claim it’s fine. I figure why replace a battery over the start/stop feature that I don’t want anyhow?

joshg1001

this! start/stop stops working, then you know!

2012 merc amg

But my point why replace a battery over just the start/stop feature not working? Everything else works. It's good to have the start/stop feature disabled, I'll take it. lol

The_Judge

Shot in the dark: Have you tried pushing the start/stop on-off button?

2012 merc amg

Yes that’s what I always did before start/stop defaulted to not working. Everything else works fine distronic, brake lock etc. seems like in the cars that use the aux battery these other things don’t work plus you get the aux battery malfunction on the middle display.

E300-18

Do you happen to know what the aux battery does? If my main battery is good and the aux battery goes bad, what is the effect that I would see?

My car is five years old, and I haven't noticed any battery issues. The start/stop feature doesn't activate very often, which doesn't bother me. The fact that it still activates occasionally makes me feel more comfortable that things are still acceptable.

2012 merc amg

At least with the newer cars in e class 2017 and up use a little black box buried inside the passenger footwell. My understanding is when these go you will loose adaptive cruise and the brake pedal lock up feature and start/stop totally plus get a message on the dash saying Aux battery malfunction. I guess these can go out anytime over 3 years or so so that’s why I bought a spare to be prepared for when it does go. I do like this setup better than the small aux batteries used in other models like my 2018 S class. They are definitely only good for 3 or 4 years and even more tricky to swap out. I got the one for my e class 30 bucks on Amazon. The battery in my S class was 100 bucks at batteries plus and then an independent place charged me 100 for the install. So in answer to your question these aux devices control some of the secondary feature of our cars. I don’t know the answer as to why these can’t all be controlled by one main battery but I sure wish they were it would make life with a Benz less worrisome and simple. If anything Benz should have not buried these 4 year maintenance items making them so inaccessible. Maybe it was a plot to get people to get rid of their cars every 4 years or so and buy a new one. If I were more young and adventurous I might just run the positive and negative wires of the aux battery to the main battery and see how that worked out and then only have one battery to worry about like most cars.

joshg1001

I know the aux malfunction message is quite common. interestingly, I did get that message maybe a year ago and it came on a few times, but then it went away and never came back.

Long Islander

You mean "charge battery" not "change battery" right?

Long Islander

What size battery did you replace the original battery with? I noticed some sites list an H-8 battery as fitting, but I don't see how it would fit in the small space on the passenger side of the engine compartment.

Long Islander

Is this what you bought from Amazon?

2012 merc amg

No I bought this one. Boskavalo voltage converter module. Looks like the one you posted should work though.

looks like they are all similar. A lot say they will only work up to model year 2018 but also list they will work with the E450 which didn’t come out until 2019. I leave it in the car so when I do get the aux malfunction warning eventually I’ll find a Indy shop to swap this part out. Simple one wire plug to install it. It’s just you have to take apart the passenger side footwell panels to get to it.