I was always under the assumption the fob batteries were rechargeable, that was the point of the docking station
After reading the advice above I removed the battery, much easier than doing it on an X Type fob. Tested the battery with a meter, its a fraction over 3 volts, the reason for this is the cell is a lithium rechargeable. I could recharge it if I had a charger to fit.
After cleaning the cell and the terminals and bending the one that sticks up from the circuit board in a bit, refitted the cell and now works perfectly In fact a bit too well, I can unlock and lock from inside the house through a window and around the corner in front of the garage where the car is parked out of sight about 50 foot away.