wirepuller

I have a toro Z-287 with the Kawasaki twin cylinder water cooled engine. The charging system is giving me a fit. I had a bad charging coil (stator) and replaced it with a new one. Upon its installation, the voltage regulator melted a hole in the back of its case and it was replaced. A new battery was also installed at this time. The contacts for the stator on the inside of the flywheel were cleaned, the contacts on all the electrical connections cleaned (battery/plugs/etc), recrimped all ends of the battery connections, checked the fuses, verified battery voltage with a meter as well as electrical output of the stator. The mower will run for 30 to 40 minutes with a good voltage indication of the guage, then suddenly the guage nosedives and the mower quits. There seems to be no short or drain on the system that can be found. And heat was also considered, but after allowing the unit to cool completly and not charging the battery, upon starting again the unit will run less than 5 minutes. I am at my wits end here. Should be a simple and nearly idiot proof system, but apparently not. Anyone with ideas?