We've replaced the key battery on two different keys with new ones on a 2014 GLK 350 4matic. The "Replace Key Battery " message keeps reappearing on the central console display.

How can we clear this message, or does it indicate a deeper problem, perhaps with the Auxiliary Battery or Relay?

 

First thing to do is voltage check the batteries you are using in your keys. I have had seemingly brand new batteries not put out enough voltage to run the key. There are so many counterfeit batteries, I always do a voltage check before changing. A new 2025 or 2032 should show a voltage of 3.25 - 3.3 volts. If your batteries show 3.0 volts or lower, they will trigger the Replace Battery message. Another poster recommended using the Maxell batteries from Japan and I have had good luck with the ones that say they were made in Japan and have the hologram on the package.

I use the 2032 battery in my keys. The 2032 is slightly thicker, but the same diameter as the 2025. The 2032 is rated at 225 -240 mah and the smaller 2025 is rated at 160 mah. Either works fine in the key. You just have to push the 2032 in a little harder. The 2032 lasts longer.

If your batteries check out good, then the problem could be in the receiving antennas or the security board. My experience with the Replace Battery message is its meant to warn you before the key loses it's ability to be detected. That means it's probably the key changing a bit in the transmitted signal to the car when it detects the voltage being low. That's pretty common in a lot of electronics that rely on batteries. Is your GLK main battery fully charged? Wouldn't hurt to check that. Most Auto places will check your battery for free.

I wouldn't expect the Auxiliary battery or Aux relay to cause this type of issue, but I could be wrong. The Aux battery is meant to power the transmission fluid pump and some other stuff when the car is stopped and ECO is working. It could supply the security circuit. All the Aux relay does it ensure that the Aux battery is kept charged. If the key batteries aren't the issue, checking the Aux battery couldn't hurt, but I don't think that will solve your issue.

Good luck. Let us know what the fix was.

 

I decided to change my 3 year old battery because of time , interestingly the new HD name brand energizer battery tested lower in voltage out of the pack than the old name brand battery that came with my glk. I would also think debris could have gotten in the remote and coated the contacts of the remote lowering the voltage , maybe it got dropped into water before . .

 

Battery problem. Get your battery at a dealer, and when it goes bad next week they will need to replace it. Sooner or later they will give you a good battery.

 

After going through several different CR2025 batteries of differing brands that never lasted more than a month I too switched over to the CR2032 with great success.

 

2025 battery is what MB recommends, that's the one I'd use. They're cheap, and easy to change and should make the message go away. I wouldn't use the 2032 chips.