This thread reads like a drama, and it unfolds a plot on who dunnit to the batteries.
My guess would be to first check the reliability of the battery, i.e. new or old and whether the battery itself is the suspect. The clock - dead or alive, won't take much of the battery life unless it runs on full digital with the complete Big Ben chimes built in.
If battery is fine - then we start looking at Amp thieves or smugglers.
Hope all would end well.