pierrejoliat

My 12 without keyless go uses a 2032, it lasts around 4 years, my 13 has keyless go so takes a 2025, lasts about 18 months, I have jammed a 2032 in that key one time when I needed to for a few days, but it was very tight and bulged out the cover.

DFWdude

Same here. And I wonder what long-term damage will occur with the 3032 battery. In particular, with the 2032 in place, I notice that the contacts are bent as the battery is jammed in place. And yes, the cover will not sit flush, allowing dust or moisture to enter the chamber. That can't be good long term for such an expensive key.

With the CR2025, the battery rides nicely between the contacts, with no chance for wear. And the cover sits properly flush. I went back to the CR2025s for that reason.

Edward993

A couple of years ago, I tried the 2032, and decided that tight fit (actually, forced fit) was no bueno! It's simple: use the 2025s, and just replace when you need to.

FWIW, I notice there was definitely an improvement in battery longevity when the fob is stored farther away from the car (eg. in our bedroom nightstand vs kitchen hook, maybe a 25' difference between the two).

Moreover, if it doesn't bug you too much I've gone months with that stupid warning message to replace the battery. I personally think that whatever voltage threshold they chose to trip that message is stupidly high ...there is way more battery life if you're willing to simply cancel or ignore the dash message

Edward

DFWdude

I've written this several times in the past but there are those who don't believe me. Good to see this is your experience, too. My keys are a good 75ft from the car in the garage.

Just be sure to keep a replacement battery in the car. No wait... the battery is not needed to actually run the car. Nevermind...

cetialpha5

It's all the same for me, mine are already over a block away as I'm in a parking lot. I notice the warning gets triggered at about 3.05 volts. New the batteries are at about 3.25-3.3 volts. I think the highest I've gotten is about 3.3 volts and those were energizers. I've delayed changing them and they've gone down to as low as 2.95 volts. Usually they hit 3.05 in about 4 months or so. I buy them 10-20 at a time on eBay, usually not that much.

pierrejoliat

I usually change both batteries in the remotes when I see the notification on the dash, as NOTA mentioned, the notice goes away after using both keys to start the car, I keep the key on my dresser, in my grandmothers pewter sugar bowl now! Thanks DFW! I for decades kept the car keys and other keys in the top of my toolbox in the garage, the 13 with keyless go was constantly going off when I washed the car, lights, locks, etc. what a pain so I moved the key inside and the battery lasts longer and the car is quiet while I wash it.

Edward993

LOL! In our first couple of months of ownership I learned not to wash the car with the key in my pocket or in the car ...so annoying, hahaha!

Edward

Alandf

FWIW Dealer in my town gives the batteries out free. Don't even have to go inside, the person at the outdoor reception has them.

And.. you can't wash the car with the key in your pocket, I guess the water in the hose transmits the signal.

nota_amg

Ummm...WHAT?!? LOL!

DFWdude

Surely he jests. With the keys in my pocket, I am well within range for the key to lock/unlock the car when I place my sudsy sponge to either side of the door handles.

It's a PITA to park the car on the driveway and then leave to place the fob inside the house.

Worse if you forget to unlock the car first.

whoover

It might be true for all 212s, but it's not true for newer models. The key in the car goes to sleep after a few minutes. After almost two years, the key that's kept in the car and the spare key in the kitchen drawer have essentially the same battery condition, as measured with a very sensitive meter. But that's a 213. The downside is you have to jostle the key to wake it in the morning. Or wait for the car to wake it via NFC, which takes about 10 seconds.

But MB definitely fixed this problem for recent models.

DFWdude

Yes, we know that keys for the W213 are different.

cetialpha5

If you take it in for service, service will replace the key fob battery and not tell you about it nor will they charge you for it. So if you took it in for service after one year, they probably replaced the battery on you.

The water in the hose isn't transmitting the signal. It's just a very sensitive sensor. The blast of water on the key handle is enough to lock or unlock the car depending on how you hit. You just need the key fob nearby. If you put it in the car, it will sense that it's in the car and won't lock or unlock on you all the time while washing it.

whoover

Unlikely. Car was less than a year old when it was last in for service. Been almost a year. The battery drain on the new keys is a tiny fraction of the previous ones. If it's not moving, it's off. Makes a huge difference. And it also prevents key cloning by thieves. Security is actually the main reason they redesigned the key.

cetialpha5

They've done that to me. Only reason I knew was because I had an energizer in there and when I checked after service, they had put in a Panasonic. I think just the service advisers do it.

nota_amg

I'm not sure if it is still common practice, but when I was a Tech for Mercedes, we ALWAYS received new battery/batteries for any letter service(A, B, D, etc...) as cars generally only come in once a year for service and one year is the "estimated normal life" of the key batteries according to Mercedes. I couldn't tell you how many I've changed over the years on customer's vehicles.

whoover

In my case, I just realized it wouldn't have mattered. I have a keyring with keys I need attached to my fob so it's my habit to give the dealer my spare. In fact, it's the only time that key leaves the drawer. So I can be sure the fob I use has the original battery.

Also, I just checked them both. Oddly, the one that's been in the drawer except for a visit to the dealer a year ago is slightly lower that the one that's been used for almost two years. It's slight, and both are still showing full voltage. (It's a 3-volt battery and is considered ready to replace when it's dropped by 10% to 2.7 V.) My everyday fob battery is 3.0457 V and my in-the-kitchen-drawer battery is 3.0375 V.

The new key has amazingly little current drain and with a shelf life of 7-10 years for these batteries, I wouldn't be surprised to see them last at least 5 years.

cetialpha5

You're in the wrong forum. Probably when they had them shut off it's also saving your battery. New the batteries are 3.25-3.3 volts. I normally get the replace battery message on my W212 at about 3.05 volts. Sometimes I do and sometimes I don't and it drops lower. But I basically replace them all the time after 4-6 months. I just get a 10 or 20 pack on ebay and they're usually under 50 cents a battery so I don't even think of it. When they get a little weak, I think it's a little harder for the car to sense the key so I prefer a fresher battery. Good to know the W213 is a little better at battery management so that they last longer. I guess each generation gets a little better. The W211 was known for having bad door handles, that seems to be fixed in the W212 and now the W213 has batteries that last longer.

whoover

I know it's a 212 thread, but think that folks interested in the key life issue would like to know that the technology has been improved. It will be interesting to see when low battery is diagnosed. 3.05 seems pretty early for a nominal 3V battery, but we'll see.

DFWdude

To be clear, on the facelift W212s with Keyless GO, one can manually turn off the fobs to conserve battery life. Just press the lock key twice in rapid succession, and the LED light will flash solidly for a second to tell you the fob is OFF. Press any key once to turn it back on. My backup fob is OFF and sits in a drawer.