Is there a alternator on the boxxer or something else that is responsible for keeping battery charge. Technician was in the middle of a job and the battery just died
It has a stator and rectifier/regulator. Look in the Briggs repair manual, it will tell you how to check it. You'll need a multimeter to do so. Your mechanic can do this easily.
If not, check these out. I have a briggs too and had the same problem. Start from the battery and work your way back to the engine. Its most likely the VR that is going out or a bad battery.
Bad battery
voltage regulator is going out
bad battery wires
stator wire got cut
the magneto coils went out