Battery driven clocks are (obviously) electric. You have a current that runs from the + terminal of the battery, through the workings of the clock and returns to the – terminal. If the clock stops it is 90% certain that the circuit is broken somewhere. It is also highly likely that the fault lies in the battery housing, this could be why the clock works on its back and ceases to work when in an upright position. Try, when the clock is on its back, moving the battery by sliding it in its seat. If the battery is loose, the clock will stop as you open up the contact by standing it up sometimes it takes a few minutes for the battery to slip away from the + contact. Take out the battery and stretch the flexible terminal carefully towards the other for about half an inch. Let go and the terminal will assume a new position. Replace the battery, which should feel a tighter fit. The clock should run. Gently lift the clock to its upright position and without undue force re hang the clock on the wall. Now gravity should not force the battery away from the positive terminal and the clock should run. If stretching fails, try placing a small, piece of tinfoil, folded to a quarter inch square between the base of the battery and the – terminal (the springy one).