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A few days ago, I received a message about the Key Fob Battery is low upon startup. I ignored it as I thought it had been changed a few months back, but it kept recurring, so I pulled the battery and tested it with a voltmeter and sure enough, it measured 3.0 volts. I actually had a new one, which measured 3.3 volts so I swapped it out, then when I went back to start the car, no message!
Wow, I thought this was perhaps a timed message, but apparently, the car actually detects the key fob voltage. It's probably in the OM, but I didn't feel like digging through it. pretty slick...
I've had this happen a few times. Sometimes we buy batteries that have been "on the shelf" for a long time, other times, the batteries never were all that good to begin with. I just buy them by the dozen (have two MB's) and change them whenever. . .
Nothing wrong with your key. Something wrong with that particular battery.
. . .Nothing wrong with your key. Something wrong with that particular battery.
Yup. I was just surprised that the message was actually from a measured voltage drop of the FOB battery itself. I had assumed that it might be like the Service msg reminders.
Does your dealer replace them for you? At mine, you can just pull up and hand your key to a porter, and they'll replace it on the spot.
On a related note, your fob battery will deplete more quickly if the fob is kept near the car because they continually try to communicate. For example, we used to keep spare keys in a kitchen drawer just inside the door from the garage and we found that the batteries would die fairly quickly. The solution is to either store them further away from the car, or manually (and temporarily) deactivate the Keyless Go functionality on the fob (instructions are in the Owner's Manual).
(edited)...In my last car (of 17 years), the key would recharge when inserted into the ignition. It was recommended to swap the 2 keys every six months..to keep them both charged (a MINI).
Does your dealer replace them for you? At mine, you can just pull up and hand your key to a porter, and they'll replace it on the spot...
LOL, they probably do, but I generally try to stay away from the dealer once out of warranty. I only go when I need service. ISTR, it's part of service A & B? It's quicker and easier for me to just go to the local Walgreen's and replace the battery myself.
I'm not going to waste a couple of hours driving over to my dealer to get a free battery — I do it myself using batteries I purchased on line.
You can buy a pack of 10 of the CR2032s, which the fob for my 2018 E400 uses, from Amazon for $5.69. Mercury batteries will last for 10 years in storage. .
Ugh, just received the same message only a few days later. The battery I had installed measured 3.3v just before I put it in the FOB, but today measured at 3.0v. This was actually the 2nd battery from a 2-pack I purchased a while ago, so I'm wondering if the batch was bad? At any rate, looks like I need to visit Walgreen's again for another CR2032...
So...it just occurred to me that these batteries are supposed to be 3.0 volts. This is actually what the last FOB battery measured, though the Key FOB Battery Low msg appeared again on my dash. However, it did disappear after I replaced the battery. Do the FOBs need to be resynced after replacing the battery?
I have two brands of CR2032 batteries on hand, Energizer and LiCB (from Amazon). The packages they come in are labeled "3V" as are the batteries themselves.
Mine was apparently set to trigger at a higher voltage so it would trip the low batt very quickly. Two fixes: One is I switched from the oem 2025 batt to a 2032, which required a slight mod to the key to make it fit. Two; I started charging the batts to bring the voltage up to buy me time. I forget when it triggers but I think it was ~3.15v. So even a new batt would need a charge. My next car didn't have that issue but I still modded it to accept a 2032.
The one time I did take the newer car to a dealer, the batt chose that moment to trip low batt. They wanted $32.46 to replace it! They also said the motor mounts were collapsed and wanted $1775, and two tires for $900. The tires were worn but still legal for a while. The mounts, however, were not collapsed and they're still in there. No doubt ready to go in the near future, but still a lie.
I tried to post a pix of the price list but it seems I no longer have the option for attachments.
I notched the offending plastic. I don't have a before pix but you can see the yellow lines where I cut out, which you can compare to yours. Assuming you have this kind of key, obviously.
I've done it to a total of four keys from two cars, and it will still accept the 2025 if you want.
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