Results of test:
battery just off the charger, engine at rest: 14v
start engine:14v
two minutes later:14v
manually engage mower:14v
two minutes later:14v
two minutes later:14v
two minutes later:14v
two minutes later:14v
I tried to think if there was something different between the circumstances of this test and when I mow. i realized that during the test the key was in the mowing position. When I mow I have to start out backing the mower out of its stall. I leave the key in the reverse position. So while the engine was running with the mower engaged I moved the key to reverse, the voltage dropped to zero.
ps: after about fifteen minutes of running the engine with key set to mow, shut it off then it restarted without hesitation.