StanNH

Not a major event, but the car does monitor the voltage level of your key fob battery.

I got a low battery warning on the main display the other day. The warning stays on while you're driving, which I found annoying since it disables the digital speedometer, and won't go away unless the car is shut off for several minutes.

I called my dealer to check on this and was told it is a legitimate low key fob battery warning. I was also told it's not unusual to have to change out the batteries every 6 months or so.

So, I did replace the CR2025 battery and the warning disappeared and all is well again. Changing the fob battery is very easy and can be done in less than a minute with no tools. I will, from now on, keep a supply of CR2025 batteries on hand since I think this will be a frequent occurrence. Probably not a bad idea to also keep an extra battery in the glove box in case this happens away from home.

chicagofan00

I would find it very unusual to have to change the FOB battery every 6 months! I've been driving cars with keyless entry & start/stop for several years and not once had to have to change the battery on a FOB. Granted some of those cars I didn't have longer than a year but others I had for just over 3 years and never changed the battery.

StanNH

That's been my experience too. Unfortunately, that doesn't look like it's going to be the case with the W205.

chicagofan00

*sigh*

mikbar2

My Ford FOB batterys have lasted typically about 5 years.

islandbeef

richardamp

My Lexus fob batteries only were changed one in 7 years. Bummer if it'll really be 6 months with this car but not the end of the world.

vsnlweb

I think it depends on how close it is to the car. If the car can sense it it will run the watery down. There is a feature that you can use to shut it off tho, if you're for example leaving on vacation or something... Hold the lock key down for 5 secs I think it is, and it will disable it. You can check the manual to find out the exact length of time to hold the button down and how to reactivate it, which is not hard.

StanNH

Getting back to my original point, I don't think I've ever had a car before that actually warned you that it was time to change the battery on your key fob.

Poor battery life or not, that is a very useful feature.

Tjdehya

I don't own a W205, but I am pretty sure all you have to do is press "ok" on your steering wheel acknowledging that you are now aware that your battery is low.

Highend

I was actually emailed this from my Mercedes rep a long time ago and found it funny that I saved it. Be nice to your keys guys!

-Dont leave your Mercedes keys on top of the car or very close to the car.
A lot of people tend to park the car in the garage and place there Mercedes key on top of the car, leave in the car, on the tire or place near windshield. Do NOT do this! The sensor feedback will drain the battery.

-Use the Mercedes key fob to actually start the car now and then, placing the Mercedes key fob in the ignition and turning it over the "old fashion" way.
This will help sync and pair the fob again. *This does NOT charge the battery of the Mercedes key.

-Try not to abuse the Mercedes key.
Be nice to your Mercedes keys, do NOT throw or drop your Mercedes keys on hard surfices. This can damage, scratch or cause internal issues.

-Clean your Mercedes Key.
You clean your Mercedes Vehicle so why not clean your Mercedes Key. Our hands contain oil and dirt, so be sure the external and internals of the key are free of dirt and grime. *Do NOT get your Mercedes Key wet!

-Change your Mercedes Key yearly.
Be sure to bring your Mercedes Key to an Authorized Mercedes Dealership where we will gladly change your battery and reprogram. *Small dealer fee applies.

StanNH

Thanks for the tip.

schvamf

On my W204 both my keys started warning about the low battery just over a year old. The strange thing is that I never even used the second key and the battery died keeping it in storage far from the car.

benzw205

Yes, thank you for posting this. So lazy i never finished to read the car manual...

eddieo45

all my MBs have had the low battery warning....

I just changed the battery in my W205 key for the first time and was surprised to only find one battery in there. All my other MBs took two. No wonder the batteries last longer in my W209, also with Keyless Go.....

flagman

That was definitely the case in my 2 W204's and I would expect it to be the same for my W205 as well. So far no battery warning so can't say for sure.

While my 2009 C350 battery went about 18 months between changes, the 2012 fob needs a battery change every 6 months or so. Easy enough to do, instructions are in the manual.

StanNH

Well, it's now one and a half years since I first posted this. Yes, the low battery warning just requires a push of the OK button to clear it. The fob batteries can go anywhere from 6 to 9 months before they need to be changed, even if stored away from the car. Changing the batteries requires no external tools, and takes about a minute, so it's not a big deal. My biggest complaint is that the fobs are not linked to the car's memory, so opening the car with any fob does not trigger the seat memory. Standing there holding a seat memory button until the seat reaches its settings can be a real nuisance. This seems to be unique to MB, since every other car I've ever driven or owned has this function.

Mikey53

Its not unique to MB, Volvo has about the same screwed up implementation, or lack of implementation, of seat memory and key fobs.


My old 2006 Acura had a perfect system in that regard. MB and Volvo, please replicate that functionality!

eddieo45

Stan, I didn't notice how old the thread was when I revived it, lol! I was pulling my hair outta my head trying to open the key fob the way I've done it on 6 other Benzes since 2003 and hoping to get a clue!

BTW, when you say "every other car I've ever driven or owned has this function" I assume you mean to exclude the Datsun 2000 and Mazda Miata but did the Z3, A4's and S60 really adjust your seat based upon which key you carried??

flagman

Agree 100%. This feature worked great on my 2005 TL. 11 years later MB still hasn't added it.

JBMCL

I thought it'd be quite common with cars that offer comfort access. I had a 2010+ Camry with comfort access and it displayed low-battery warnings for the fob.

StanNH

I should have qualified that by only including my cars that didn't require an actual turn of a key to unlock the doors. :-) My A4's and S60 did have the seat memory synched to the fob. MB really does some odd things with their electronics. I still don't understand why I have to scroll off the speedometer screen to see my odometer. That makes no sense to me at all.

Luton Driver

The W205 keyfob seems to have an unhealthy over range to unlock the doors or to release the boot. It must be at least 150m and that is even around corners. No wonder thieves with laptops are managing to steal the codes as they don't even have to be close to the car.

storm10

By the way, you can always open the door and start the car... even if your Key-fob is dead....

benzw205

I wonder if thieves have all the codes for all the new cars ? Any report of a C-class stolen without being broken ?

Thanks.