I got this weird problem on my car.

When I press the remote key to unlock the car, it unlocks without problems. But when I press the red button to lock it, nothing happens.

I can, of course, lock the doors manually so it's nothing too urgent.

I only have one key left so I can't test it with the spare key.

Could this be an indicator of key battery power (too low)?

Thanks in advance.

try changing the battery of the key. i remember mine had similar problems when the battery was almost dead.

also after you change the battery, you will need to reprogram the key.

Good luck!

I changed my battery and didn't have to reprogram. But yes, battery is the likely solution. Less than $10 at CVS.

I had this problem with another car I had and after taking apart the key fob I found there was a very tiny metal disc that acted as a spring against a contact below it. I think the piece either broke or became dislodged, so the button simply did not work. I managed to get it working by somehow taping it together, but it was dicey. I immediately sold the car before it broke again or the tape let loose.
I'm not suggesting you sell your car due to a bad keyfob button, but if that is your problem then then you would need to replace the keyfob. And if you can hold off until 2016, you could sell your x-type and buy a new XE.