Verify that the battery voltage is getting to the clock mechanism. These things are built down to the lowest possible cost and oxide layers on the battery terminals or other similar problems often causes failures in these.
Next place to look is at the motor stator itself. Often you will find it twitching, but not turning. Things have worn enough that the proper geometry is not maintained or it is physically rubbing. When this happens I have found a "new" mechanism is the only good solution. I do look at thrift shops for clocks that are either out of style or have water stained faces and find usable mechanisms for far below new prices at domestic sources. Ali Baba will have truly new units for dirt cheap prices.
While the physical outline of the movement is well standardized and almost all are interchangeable, the shaft diameters for hour, minute and second hands are not, so either care in acquisition is required or some careful bodging to come up with a workable combination.