nc211

I think it’s about time for a new main battery in my W212 (sedan / 350). Everyone fine with aftermarket or should I stick with OEM. It’s 6 years old and noticed last night that the radio won’t stay on for more than 15 seconds or so without the engine running (which is a first). I suspect the battery is getting close....

I’ve replaced the auxiliary a couple of times over the past 3 years, no big deal. It’s relatively new (yet I hardly ever get the green light for eco start/stop in general).

MB or aftermarket? And what’s this “reset” business about? Mine is a 2014.

many thanks!!!

LILBENZ230

You should be able to replace it yourself without issue, and aftermarket should be fine. Note - the eco stop/start system is dependent on the main battery, it is not tied to the Aux battery so if that system is never active then yes that is a sign of a weak main battery.

KEY08

lots of battery threads on here. Buy the best and most economical AGM that meets the criteria. No need for an OEM battery. Your ESS system is not working because your Main battery is going South. Replacing the main battery will get your ESS up and running again, whether you want it to work or not. Nothing to reset.

Arrie

Just a word of caution. I replaced my battery at AutoZone when I had issues with low charge (that was actually a starter problem).

Anyway, AutoZone installed the battery and the guy used some sort of a “battery” connected to the OBD port while the main battery was disconnected. He said this prevents the car computers from losing memory.

A few months later I went to get the car inspection but they could not read the codes. Turned out the fuse for the OBD port was blown. I think that “battery” that AutoZone guy used caused this.

I have disconnected my main battery several times after that when working on the car and never had any problems and have not needed to reset anything else but seat memory positions.

mellonc

same here. I did it myself in about 20 minutes. I needed a helper to pull the existing wires out of the way when I dropped the battery in. All memory settings came back normal when I restarted the car.

ItalianJoe1

In cars with the larger aux battery (the powersports battery in the trunk, not the tiny one in the dash), that battery is 100% used for eco stop/start and a fault for it will disable the system.

ItalianJoe1

The reset is for the digital control of the alternator and the adaptive charging system. The power management functions charge the battery more slowly as it ages, and when you replace it you should tell the computer that you did so you go back to full power charging and don't unnecessarily shorten the life of your replacement battery. I have posted the function doc here for the system before with more detail, but in general, the car only attempts to charge the battery to about 80% to leave some room for energy recovery from the alternator under appropriate conditions, to improve economy. If the car assumes the main battery is from 2015 still, it will be charging it much more gently than it could and it may never be close to full charged after you install it.

KEY08

but isn’t the main battery the only battery used to actual drive the starter during all starts including Eco? We have had several threads that continue to point to the main battery when Eco start/stop fails to engage ( not meeting all of the parameters). End users replace the main battery and things go back to normal. I’m so confused.

ItalianJoe1

Read the attached GF doc in this thread.

The small battery is used to maintain voltage when the car is cranking. If it doesn't pass the check, the car won't shut off. There are about 80 parameters that can disable an eco stop/start action. Either battery can be the cause.