Mercedes C Klasse Key Battery Issue

I had a similar problem with my old BMW. The car key was practically dead. Did you check the battery voltage with a multimeter to confirm low voltage? Sometimes it's not actually the battery, but a problem with the key itself. A battery replacement is the first and easiest thing to try though.

Thank you for your input. I did not measure the voltage directly. I assumed that the error message was accurate. Where exactly did you measure the voltage on your car key? I'm unfamiliar with disassembling the auto key and would prefer to avoid damaging it.

On my BMW car key, I carefully pried open the case – there are usually small slots for a screwdriver. Then, I measured the voltage directly on the battery terminals. However, if you are not comfortable with that, I would recommend going to a workshop. They can replace the battery and ensure the key is still functioning correctly afterwards.

Thank you for your advice. I followed your suggestion and visited a workshop. As suspected, the battery replacement, costing approximately 37€, resolved the 'key battery low' issue and restored full functionality to the car key. It was indeed a simple battery replacement.