kevm14

My dealer parts department handed me a 5 pack of Energizer 2025s last time I asked about fob batteries.

W205C43PFL

not quite sure but does this generation have the feature when you double press the lock button on the remote it disables keyless go?

Yakatak

Yes.

cetialpha5

I think it depends on the year. Some of the early ones don't do it. The latest is that it shuts off after 5 minutes when it detects no motion. You could always put it in a faraday cage which is basically a metal box. Lots of them on eBay/Amazon.

2013LBCoupe

This along with others I heard from here tells me the Energizers are the better buy for our 2025 battery replacements.
Thanks👍

2013LBCoupe

Thanks for the buying tips...
And by changing out the batteries before they die, you mean you change them as soon as you get the "Replace Key" warning...correct? I had waited to long to replace mine after the warning --- not a good experience.

W205C43PFL

I see.

W205C43PFL

I see.

W205C43PFL

Good advice, in terms of Amazon I wonder if those Sold and Fulfilled by Amazon are less likely to be fake, I mean I get it there are some sellers that are sold by them but fulfilled by amazon still run risk of being fake.

kevm14

I bought my car recently with TWO totally dead fobs. I replaced the battery in one and it worked immediately, no other fiddling required. I didn't check the other one but didn't want to put a brand new battery in it and have it just sit unused and drain. Or maybe I did test it and then removed the new battery. I forgot already.

W205C43PFL

If it is confirmed it isn't a bad battery, might want to consider using some electronic cleaner to clean the contacts.

kevm14

FWIW, my 2005 Cadillac STS also had a similar system to Keyless Go. I think one time my wife borrowed the car and used the spare key. It wasn't working. I replaced the battery and it still didn't work. Then I checked both batteries, old and new. The old battery was fine! Ended up cleaning the contacts in the remote and that totally fixed it (on the old battery). So yeah, that is definitely a thing.

W205C43PFL

I see glad it worked out for you did you use electronic cleaner or something else (like I don't know distilled water? although I don't recommend any water only because even for distilled water, it can easily get charged with some sort of ion contact, putting our hands in distilled water can likely make the water ionized and therefore create short circuit for example)

kevm14

I used Deoxit. Can also use isopropyl.

W205C43PFL

Ah good choice.

JimFE

Finally got some time to deal with this. I decided to first try and pry up the contact terminals that the battery rests on. Used a flat mini screwdriver to do that, and was able to move them up about a half millimeter or so. Put in a fresh battery as well, the one I pulled out was a Panasonic and measured 3.02V. Replaced it with a Li-Cb from Amazon which measured 3.26V. At the moment it is working fine. We will see how it goes over the next days.

W205C43PFL

I see so not due to oxidization/oxidiation but actual mechanical weak contact between the battery and the pins.

cetialpha5

When I've changed the battery after getting the low battery warning, it's been at 3.06 volts. If I delay a while, you don't get the warning anymore and I've had it at under 3 volts.

Amazon is supposedly getting better with fakes, but what they do is throw in all the merchandise from various vendors into one bin so all you need is one vendor with fakes and you end up with fakes even when you think you're buying directly from Amazon because they're throwing what they think are all legitimate products into one bin so the fakes mix in with the real ones.

Yeah, no water, you certainly don't want rust to appear. You basically want something like contact cleaner or whatever that dries out completely and doesn't leave any residue behind.

I also wonder if it's due to brands and in theory all 2025 batteries are supposed to be the same but maybe some are off one way or another by just a tiny amount. I've had to fiddle with one remote with various batteries but I just did Panasonics and they worked fine after replacement. Or maybe the last time I played with the contacts I've got them in the right spot now.

W205C43PFL

Yikes, I guess still can't trust Amazon... I guess there is not a dedicated team to confirm the authenticity of the battery/products in general before just tossing them all in.

I see, and it can be both.

JimFE

That is the theory I am trying to prove (or disprove...) The contacts looked very bright and shiny (will take a picture next time I open up the fob)

JimFE

I don't think so. I get the same behavior with generic Amazons, and first quality Panasonics. I've been measuring the voltages when new, and when they start misbehaving, both brands have been coming in around 3.26V when new, and start to crap out around 3.01V, when KeylessGO stops working (though the buttons still work)

W205C43PFL

I see, let us know.

JimFE

I think I have solved my problem. As a part of my latest B service, the main battery was shown to be weak. After replacing the battery, my “cranky” key fob has worked perfectly for over a month. The auxiliary battery now needs to be replaced (I’m getting the “auxiliary battery malfunction” message regularly), but it apparently has nothing to do with the performance of KeylessGO.

Chevota

I had the same issue and it was the battery voltage of the key. With a new batt it took a couple months to a little as a couple days to die, which depended on the voltage it had going in, which was likely the quality and time passed since it was made. The chrome sided key btw. Not sure what years those were made but certainly used in my '13 & '16. Oem it takes one 2025 3V batt.
When it dropped to ~3.05V I'd get the warning on the dash. Weird how a 3V battery at 3V doesn't work for it, but then a 12V car batt is kinda deadish too if it's 12.0V, but at least it still works!
So I started charging the battery myself, topping it off so it was no doubt better than the day it was made. I forget exactly what I charged them to but I believe 3.4V, maybe as much as 3.5. That solved the problem in a nutshell. I also replaced the 2025 cell with a 2032, because I'm one of those people that loves to modify things for the better. It takes a little trimming on the key to make it fit, you can't really tell once done, and a 2025 still works if you want. I took a pix of what needs to be trimmed, which I can dig up if anyone is interested. It's also posted here somewhere on a thread where someone had the same issue.
The bigger batt and top charge is so effective that I can't for sure recall the last time I did it, but it's a hella lot longer than before.

I know 99% or more people will have zero interest in charging the batt, but for the few that are:
Since the batteries are very small you need to charge them very slowly or you'll screw 'em up. I forget the current I used but it would certainly be <20mA, probably more like 5. At that rate it might take a whole day to get 3.4V from a "dead" 3.05V batt. Voltage of the batt will climb as you charge and I'm not sure where it'll stop if you simply left it on charge, but since I didn't want to exceed 3.5V, for the keys sake, I'd take it off charge and measure now and then.
If I recall correctly, the first time I did this I used AA batts (3) as the power source, and next time I used 5V from a USB port, which I think was really 5.5V? Plus a resistor to throttle it down, of course. I suppose 330ohms should do the trick. The lower the current the easier it is on the batt, so more than 330ohms is fine, even 1k or more. Just be sure you measure the current, in case you made a mistake. Don't want the thing blowing up during the night
Or you could make a 3.4V charger, if you were so inclined, which is probably what I should've done first, and will do next time.

You can charge the battery more than once. Lithium doesn't seem to mind being recharged, but I don't know how many times before it degrades. I had a few little flashlights that used a 2032 non-rechargable battery and I topped them off dozens of times. Some 2032 batts say "Rechargeable" on them, and I've had a few, and I can't tell the difference. My guess is there is no difference, but they'd prefer you don't recharge them so they can sell more.
Alkaline, on the other hand, like a typical AA, I see degradation the first recharge. More the second, and so on. So for those I usually only charge once or twice, then toss 'em. In case anyone was interested, because I hate buying batts all the time so this basically doubles their life. Think of the environment, you're recycling first hand

CaliBenzDriver

For owners who have a bone in this fob ordeal I am going to chime in with a hint at battery drain correlation.


Sleepless fob battery...
Fob batteries can last a long time if they are allowed to sleep - The fact yours doen't proves it is overworked. I used to have that ridiculous nightmare...


Distributed control...
Our key transmitters chat with antennaes scattered inside and outside the car. These connect to a keyless module that networks with Ignition Key module that authenticate ID's to enable activities


MB Keyless chaos...
The keys and antennaes work fine. The issue is with the marginal Keyless module interfacing over a busy CANBus jamed by goofy DCU traffic to the crazy EIS Module gone wild.

This generates boat load of retransmits the coincell in the fob pays for.


Non-stop...
The fun doesn't end when you shutoff the car. The main battery pays for sleepless system waking up for prolonged periods and draining the starter battery. Same polling game retransmits except car modules drain more power than tiny fob.

Best practice is to float-charge your main battery as needed to preserve it from going too low.