My experiences? Had a few, but a closely related one goes like this:
Climb to the altitude where the unpressurized fuel (fuel boost off) starts to 'boil'. Shut down turbine engine and try restarts to determine highest altitude at which the engine will start. 1st attempt, hot start. 2nd attempt, hot start, 3rd attempt, Uh oh. ICS went dead, gyro tumbled, lost all electric instrumentation. Intinctively, I keyed the mic and declared a Mayday, again and again. Got no response. A check of the battery voltage showed a big fat zero. (Found out later that it had a dead short). Got a visual on our home airport and silently headed on down.
Just for reference, we had been operating at altitudes between 22,000 and
25,000 ft. unpressurized and without any O2 on board. Easy to do if you breathe real slow and real deep while there, but only fora limited time.
Finally, after that very long descent, entered the left crosswind leg at which point I actually opened and began yelling out the side window 'Mayday, mayday, mayday - engine out'. Of course no one heard me, but we laughed as we did the LH pattern to touchdown which turned out to be a bit short of the runway. More laughs.