I started getting a "Key Battery Low" message at startup, so I bought new batteries for both fobs. The error message continues.

Any idea why this is?

 

Get a multimeter and actually measure the voltage. A new batter should be around 3.3V. You'll get the message at around 3.0 V.

 

I think the InstrumentCluster display message needs to be reset manually.
I recall a ridiculously complicated push button procedure to reset what has been automatic for decades on HondAcura.

See WIS or YouTube...

 

I don't need to reset this message. It goes away with new battery in the key.

OP, you probably bought a low new battery. These batteries have shelf life and sometimes you just buy a battery that is already low.

Also, the key fob comes with CR2025 battery, but I started using CR2032. It is a snug fit and I need a tool to get it out, but it gives a lot longer battery life.

 

I tried the other battery and it works just fine, so I think you are right. I had one low battery.

 

Yes, the keyless stuff is very voltage sensitive.

 

The dealers for all three of the makes that I drive, MB, BMW & Porsche all provide free key fob batteries and installation at the parts department.

Since they install so many, their batteries are fresh and always work well.

You might want to try your dealer's parts department next time.

 

2032s can give you more extended battery life but I stick to 2025s , I stick to the manufacturer's recommendation .Good to hear new battery works fine for the op as well

 

That is nice, mines charge like 5-8 dollars a pop.

 

I get bulk batteries on Amazon. Also, if the CR2032 fit, they should be OK since CR2025 and CR2032 are the same voltage. I personally wouldn't want to put the extra pressure on the circuit board in the fob squeezing in a thicker battery since the fobs are so damned expensive! Over time, the thicker batter could cause the PC board to bend or crack, damaging the board.

 

Ah, I knew that number sounded familiar. CR2032 were used in Tamagotchis my kids used to play.

 

Fwiw, the dash throws that low batt warning far to early IMO! I have gone months --yeah, many months-- with the same battery after the first warning. Only when the keyless entry got intermittent, like took a second touch of the handle to unlock the door, is when I finally replaced the battery. I wish I had recorded how much longer I got, but it was easily over three months more, if not longer. And even then, I should have logged how often keyless entry was intermittent. Maybe the next low-battery warning I will do just that. I know a CR2025 is cheap, but I feel stupid throwing away money because the factory told me to.

Edward

 

The 2032 battery goes in the R232 key fob.
Here is an excerpt from the owners manual for replacing the fob battery…

I probably should try to post this in an appropriate R232 thread, while I am thinking about it as well.

 

I mentioned this on another "Key Fob" thread, but repetition is free, so:

Try "tightening" the positive battery contacts. Remove the battery. You will see a shiny battery contact in the battery compartment. Using a small tool (I use a dental pick), gently lift each of the four contact tabs away from the circuit board a bit. They should remain just a bit "higher" than they used to be. Re-assemble the fob with a known good battery. The contacts will now have just a bit more pressure onto the battery, making a better contact and getting the battery's full voltage to the circuit board.

I've used this on two 2015 MB's -- a GLK and an E-Class. Worked on both.