My original key went dead some time ago. Now I have a problem with my spare key. There is no IR light emitting from the key fob, so the doors or windows are not responding, Thankfully, the key starts the car and and the door knobs are all operative. Any DIU suggestions here. I have a new and tested battery in the fob.

 

I had similar and went to a Merc dealer, they asked me if I bought a genuine Merc battery …….NO, but a good make, I said. they sold me a “Merc” battery and it worked ok. Buggered if I know why🤷‍♂️

 

Thanks for your suggestion. I replaced the key fob battery with the panasonic battery recommended by MB and all is well now. How strange...............