Mini Countryman key battery low warning

Sounds like a dead key battery to me. I had a similar issue with my Mini Cooper, although it wasn't a Countryman. Did you try the spare electronic key to see if it's the same problem? If the spare works fine, then it's almost certainly just the battery in your primary key fob.

That's a good question. I haven't tried the spare yet. If it is the battery, is it something I can replace myself, or is it best to have a professional handle it? Is there anything special about the auto key I should know?

Yeah, sounds even more like the battery now that you describe the symptoms. While you could try replacing the battery yourself, these electronic keys can be a bit fiddly. You don't want to damage anything. Honestly, for the cost, it might be worth just popping into a workshop to have them take care of it. They'll be able to confirm it's just the battery and get it sorted quickly.

Thank you for your assistance. I took it to the workshop, and as you suspected, it was the key fob battery. The auto key is working again and everything is back to normal. Repair cost me 37€.