cetialpha5

Yeah, but I got Energizer batteries before and they only lasted 4 months, same deal as the dealer Panasonic batteries. Never had mine last more than 6 months. Don't know if it's because I'm in the city and there's lots of other signals/cars around which make them work more than people who may live in a quieter suburb.

Zavato

I use Panasonic batteries. I replace the batteries in the 2 key fobs once a year, and have never had a battery go dead on me. Easy!

kajtek1

I search the net and can't find solid answer if the key is on stand by mode when outside the car, or it shuts itself off. Did anyone actually try to see if keyless go would work with dead battery? I still "want" to believe the batteries are only for the remote buttons.
So far my keyless go car is garage queen, but 6 months after purchase battery still work.
Found interesting article on the net:

How to Use Mercedes-Benz KEYLESS GO®

With Mercedes-Benz KEYLESS GO®, you can unlock, lock, start and stop your car or even close your windows and sunroof from the OUTSIDE of your vehicle, simply by having your Smartkey in the immediate vicinity of your Mercedes-Benz.

To unlock your car, firmly grip the driver door handle. To unlock all doors, grab any of the passenger handles. Most models have a removable push button located in the ignition and the dash that allows you to insert your Smartkey and use it as a regular car key.

If your button is in place, each press is like turning the key one position as long as you don’t press on the brake. With one touch you can turn on your vehicle’s accessories such as the radio.

Press the button a second time and the dash lights and all electrical items will turn on.

Press a third time with your foot off the brake, and everything turns off. You can also turn all features off by opening your door.

To turn the engine on, simply step on the brake and push the START/STOP button. To turn the engine off, stop the car, leave your foot on the brake, and press the START/STOP button once again. Remember to always shift to park and set the parking brake first.

If you want to lock your vehicles from the outside, simply touch the sensor located on the door handle. Forgot to close the windows and sunroof? No problem. Keep your finger on the sensor until the windows finish closing.

thenew3

I just tested it. Removed battery from my key. Keyless go stops working completely. Cannot lock/unlock door or start car with push button. Car starts fine if you remove the button and insert key into the hole in the dash.

DFWdude

Update... I had my car serviced for other reasons on Monday. While there, I asked my SA about this keyfob battery drainage issue. Both the SA and the Asst. Sve. Manager told me to store my key fob as far away from the car as possible after locking it.

"The car is on all the time," they said. "And if the car senses the key fob is within range, it will drain its battery faster." They added, "For sure, do NOT store your key fob in the car, or within the garage where it's parked."

Mercedes has offered Keyless Go in their cars for several years now. One would think the dealers have dealt with this question for the same amount of time and know what they are advising to customers. Believe what you want, though.

I keep my key fobs in my bedroom, one in a dresser drawer with all the other backup key fobs, and the other on top of the dresser. The dresser is probably 25+ yards from the car in a detached garage. The batteries in my key fobs are OEM to the car, built in July 2015... nearly 4-years ago.

Believe what you want, and do what you want, of course.

kajtek1

So the keyless go knob I got with the car is still alive after 6 months and I don't know how old battery was in it. We drive the car like 1-2 times a week, so that has to be a factor?
I am on the market for spare key. Anybody know better source than $380 (+ programming) at California dealer?
BTW the dispute about putting key far away from car reminds me several topics about Bluetooth in W211 section.
Similar if your family room sofa is close to the car, it is the car who is going to answer your cellphone.
I had my W211 park next to a camper I slept in and getting up in the morning I noticed Bluetooth puck in the car still active.
Good procedure on older cars was to observe cluster and interior lights to go off after 10 seconds from closing the door.
Now I need to ask DW to take keyless key (!) away and observe the lights.

thenew3

I did an experiment a couple years ago. Took my two key fobs, put in fresh batteries from same batch. Locked one in a safe in the bedroom about 50 ft away from the garage, put the other one in the key jar just inside the house about 15 feet from the car.
Both fobs gave me the low battery message about 6 months later. So as far as distance away from car, that doesn't seem to make any difference in terms of battery drain.

konigstiger

Or deactivate (2016 manual)...

kajtek1

Check manual for my 2014 model and no such option. Will play with key later to see if that might still work.

konigstiger

Replied toDFWdude dealer's comments, couldn't be more clear.

DFWdude

Konigstiger, I forgot about the ability to de-activate key fobs. I have now done so with my backup fob in the dresser drawer. Thanks.

Something in return for you, "King Tiger".....

DFWdude

Sorry to distract with my previous. Let's return to the topic.

jumpman726

You might be able to find lithium CR2025 batteries at Dollar Tree. They used to come as a 2-pack, which comes out to only 50 cents a battery, but they might be switching to single packs. The brand is Sunbeam. It's what I've used the past several years.

DFWdude

Since the fob I've used since acquiring the car 15 months ago is now showing the "replace battery" notice, I've planned to buy some replacements.

Today I stumbled across a 4-pack of Lithium CR2025s at Harbor Freight. I was more attracted by the "Lithium" label than the blue packaging they came in which reminded me of a brand name... only when I got them home did I realize they were "Thunderbolt" brand LOL!

Anyways, they test very strongly -- well above 3V -- so I will give them a go.

I suppose there should not be any problem using lithium batteries?

cetialpha5

CR2025 are lithium batteries so you're fine.

DFWdude

D'oh! Thanks.

swilkins56

I'd suggest calling dealers in states that have no sales tax...and verify that they will ship to you(security readons). I paid $250ish in LA,

kajtek1

Is it $250 for keyless go?
About 7 years ago MB USA judged keys theft-prevention item and no longer allow shipping. Some dealers actually require car to be present before giving the key and for keyless go you need to program it anyway.
Since I posted the above, I was visiting California and went to dealer who sold me regural knob for $162 few years back. Now keyless key (how stupid is that?) with programming cost me about $500 but they include checking the tire pressure and resetting TPMS.
Obviously coffee and bananas

KEY08

Bananas too? I get bad Keurig coffee and Nature Valley Granola Bars at the dealer.

marathonrunner

I bought my 2014 a year ago July. Drive the car basically every day, key is in my pocket or on my dresser. The battery in the fob worked for about a year before the replace battery notice. The new battery only lasted about 4 months. So I put a new one in last week, and got another replace message in 2 days. Even though I have the KeylessGo, I didn't think the battery should have been drained THAT fast. And they weren't old batteries. So I started poking around the compartment and noticed the contacts for the wafer are on the bottom and on the edge. The metal is very springy of course, but I was able to carefully tweak (bend) the contacts just a little for better contact with the battery. Message has not come back since. Not saying it's a cure, but seems to be working for me.

Los Gatos Guy

I have a 2015 C300 W205, 2 key fobs, Keyless Go. This year started having very short battery life and then replacing the CR2025 battery would not clear the warning - keyless still worked.

Tried Energizer and Maxell batteries, both with 3.25 VDC before use, no luck

I tried bending the 4 small battery tabs up before insertion - no luck.

I tried the battery remove/replace in the car after starting had no success.

Then I tried the suggested replacement of the CR2025 with a CR2032 (20 mm diameter and 2.5 vs. 3.2 mm thick), tight fit but success on both keys!

What do I think the problem is? I would take the fob apart and try to perform a failure analysis, but a new, programed key from MB is $500+. From my background in PCBs and Failure Analysis, I think the small metal part that contacts the bottom of the battery also contacts the printed circuit board to make the battery connection to the circuit. These PCBs are inexpensive and the surface finishes are not very durable - over time the contact may be oxidized or worn and the extra thickness of the CR2032 battery increases the contact force that reduces the electrical resistance. This fix will increase the apparent voltage to the circuit and it will no longer think the battery is weak. The voltage difference between a good battery and a weak or dead battery is less than 0.5 volts, a poor contact can easily generate this type of voltage drop.

The upside is the 2032 battery will last longer, the downside is that it will be harder to remove when it has to be replaced.

Thanks for all the other posts on the internet that helped me find a fix for our car!

DFWdude

As noted in post #39, I replaced the battery in June, 2019, after more than 15+ months without issues. (That's 15 months after I acquired the car... I have no idea how many months before the battery lived in the car before I bought it.)

It's now been 15 months and counting on the replacement, and the fob battery is still going strong.

Tirgoman

I've never had a problem but maybe a tiny dab of dielectric grease on the contact would prevent oxidation. Failing that there is conductive grease, s very tiny dab of that.

Los Gatos Guy

Our keys were fine for the 1st 2 years, then they were not.

nota_amg

CR2032 FTW!!!

Replaced the 25's w/32's almost 2 years ago...no issues since for me.

Just curious, but did you replace the batteries in both keys, then use both keys to operate/unlock/start the car separately? My wife's key battery was low, but mine was not. Even though, when I used my key, I would get the "low key battery" warning in the dash. Changed my batteries and I still got the message. I had to change her batteries, get my key away from the car and use hers to open/start the car, then the warning went away.