I have a 2013 c250. the key fob door lock/unlock has always been weird since we bought it. When we bought it the guy said he changed the battery and he did but broke the back cover. I have moved the prongs out to make better contact with the battery. Replaced the back to make it hold better. put a piece of tape on the back and we even got a silicon cover on it. It picks and chooses when it works and when it doesn't. I really don't want to get a new key as this one looks great.

any advice would be great

It may be the internal motherboard on the remote but have you tried a thicker CR2032 battery? It is the same voltage (3v) as a CR2025 but is a little thicker and longer lasting.

The CR2032 fits very snug and could alleviate the loose contact on your battery/remote.

My girlfriend has a '14 C250. The fob stopped working (lock/unlock buttons didn't work), so she shifted over to using her other key/fob. I replaced the battery in the "dead" one, but the lock/unlock buttons still don't work. Is there some sort of "re-learn" process that you need to do with the key/fob when you replace the battery?

I have not checked to see if it still works as a key. And I will confess that I have not cracked open the Owner's Manual to see if there's anything in there about replacing the battery in the key/fob.

I asked my gf to unlock the car with the other key/fob, then test the key/fob with the new battery to see if it would start the car. Yes, it would, and after doing that she said it now locks/unlocks the car just fine.