Got the “replace key battery” warning in the MFD on Monday. I replaced the battery and had 24 hours without the warning. Today I went to start the car and the battery warning popped up again.

any idea what’s wrong?

 

Check the charge of the battery. They do have a shelf-life.

 

Like what DFWdude said, check the battery. There are a lot of counterfeit coin cells out there, because it's so easy to make them. Basically, if you pay less than $2 per coin cell at retail, you can be almost sure it's a counterfeit or some crap brand that won't have any sort of service life.

 

I got the battery from the dealer but I’ll check it anyway. Thanks everybody!

 

Always keep some on hand as well I just changed one the other day and the car still had the message, changed it again and away it went

 

I get the replace MFD message and it hasn't gone away after replacing the battery. I checked the new battery and it's 3.2V, and the key starts the engine and unlocks the doors and trunk lid just fine. Would the recent change in weather (colder) have anything to do with it? The temp was in the 20's overnight, and was around 35 when I started the car this morning. It's still cold midday, around 35 degrees.

 

Change the battery in your other key... seriously

My Wife's key was setting off my indicator on the E. She didn't even drive, just parked next to me in the driveway...

 

nota_amg, I see how that worked in your circumstance -- clever to figure that out. It's not the problem with mine. My other key is not in use and is protected inside a shielded pouch from activation by malign actors (car thieves)..

 

Clever deduction!

 

yeah, that one threw me for a loop and had me scratching my head for a few days.
Even if it is hidden away, might not be a bad idea...just to rule it out...you never know. Maybe you bag isn't working...

 

My local MB dealer replaces them gratis. Always does both at same time,

 

Are you DFWdude's brother???

 

Let's not get started on the sugar cube bowls again! LOL Since Marvin is moving from trunk lid to bumper, we may have to get him a housewarming gift!

 

Well...

Well...

Well, I may have a few Faraday Cage bowls sitting around. But I do NOT keep a handful of 2025 batteries and a voltmeter in the center console. OK?

 

LOL!

 

Don't laugh My house has a stucco exterior which is installed over metal lath (I guess to give it strength) . My entire house has become a faraday cage. Great for key remotes. Not so good for cell phone reception.. I have to stand near an open door or window to get a good signal.

 

Bowls not necessary:

FobGuard Security Pouch - Ideal Faraday Cage to Protect Car Keyless Entry Fobs from Hacking, Signal Amplification and Signal Relay Attacks

 

Amazing. I bought a "two-pack" of that exact model.

Have you tested it? Cause it DOESN'T Work.

Before we drift far afield again, check out this thread... https://mbworld.org/forums/e-class-w...ml#post7868809

 

DFWdude, I tested mine by putting the key in the pouch and tried to open the car door. Couldn't open it with the key in the pouch.

 

I did the same. If you place only the key fob, fully shoved down into the pouch, and close the flap tightly, it would block the signal 50% of the time, depending how diligently you close the flap. You can store an unused, secondary key fob this way, I suppose.

But no one places only their primary key fob in the pouch, because it is almost always attached to other keys (house/apartment key, other car keys) and items on key ring(s) that dangle outside the pouch. Tried this way it will never work, because the extra items work as an antenna outside the pouch and the flap can never be completely sealed. Not very practical for a daily use key fob.