Thanksgiving, 2011. Our 2012 GLK 350 was a week or two old. Thanksgiving is easier to remember. We were going out for dinner with friends. I naturally volunteered to drive.
Thanksgiving, 2012. The GLK 350 is a year old plus a week or two. Same plans as last year. Same couple joining us. We are driving once again.
"Replace Key Battery" appears in the center of the speedometer circle. "One year, hey?" No worries. I have spare batteries at home for this purpose. The warning was early. We parked, had dinner, drove home. No worries. Changed the battery at home. Good to go.
I find it interesting that the remote battery to go first is mine. It only gets used 10%-20% of the time. My wife's remote is used most often. Go figure.
Educated guess: The new battery bought at WallyWorld will outlast the factory original.

Wayne

 

Do you park your car at a parking garage? The reason I ask is because of you leave your key fob in the car (like some parking garages do), the key fob constantly communicates with the car and drains the battery. Happened to mine on a Lexus, had to tell the attendants not to leave the key in the car. Otherwise, I have no idea

 

My key, with the battery that only lasted a year and a few days, lives in my house. The GLK has only seen a few parking garages & the remote did not stay in the car.
I am very thankful that the dealer showed us how to replace the battery & we keep spares at the house. This forum has several mentions by folks who were charged $50 by dealers for a new battery. The shame!

Wayne

 

So I should tell my wife to expect the same message in a few months then.

 

No clue. One data point, mine, does make a trend.
After reading about various battery life experiences on this forum for various models, we bought a pair of batteries for $3 about 2-3 months after we got our GLK. Cheap insurance. Apparently, the Replace Battery warning appears well before the battery is dead. Don't ignore it.

Wayne

 

I had two spare batteries which i bought in advance.
A few weeks ago, I replaced the battery in my key and it lasted 3 days then the "replace key battery message" shows up again.
I replaced a 2nd battery, which also lasted 2 weeks and now I have the same error message. LOL
Time to shop for more battery.

 

Or a new remote if under warranty. That doesn't sound right at all.

Wayne

 

I think my remote is fine.
I think it's related to battery's shelves life.

 

Most battery packaging has an expiration date these days. Are you buying the correct Lithium watch battery?

Wayne

 

Yes it is correct lithium battery.
No, these battery does not have expiration date on 'em.

 

We use Duracell. Exp. date on the package-usually about 3-4 years out.

Wayne

 

This is going to sound crazy but on my father's E class with Keyless Go, the battery lasts about 1 year and 3 months. First time it went out we just purchased a replacement at a local store and it lasted 2 weeks. Went to another store and the battery lasted 1 week!.

Finally went to dealer and they said they're battery is "special". Charged us $15 but it's been fine for a couple months now. I know it's typical Dealer speak but maybe there's something we're missing. Good luck!

 

Batteries in general is an interesting story. The specifications with regard to capacity (mAh) (and other parameters) varies a lot between the different brands. I.e. for the CR 2025 is the Varta and Duracell typical capacity 165-, Energizer 163- and Panasonic 150mAh. Typical continuous disharge time and the shelf life are as well important for a durable battery.

So next time I would try Varta, Duracell or Energizer before the dealers choise, given the price is fair.

 

As predicted, the Spouse Units battery required changing yesterday. The GLK is pretty slick. Both Smart Keys were in the GLK at the time. The "Replace Key Battery" came on. We determined that it was her key quite easily. After a stop, Lisa got in the GLK first. Turned on the ignition. Replace Battery came on. We replaced the battery when we got home. Bought new spares today. Piece of cake!

Wayne