Step 1: Open the remote
To open the remote just remove the screw with a phillips head screwdriver and then use a standard screwdriver to separate the two sides of the case.
Once the remote was open I could see the problem. Part of the battery holder had come unsoldered.
Step 2: Soldering
I'll admit it's not very clean but it is definitely secure.
Now I just need to reassemble the remote and I'm done!