Thank you Matthew, this is very interesting data, exactly what I was looking for. :-)

BTW battery low = lower voltage, so for same output power to the motor you need more amps, hence the battery warms faster (P=U*I = R*I*I).

On Monday, September 14, 2020 at 9:31:25 PM UTC+2, wrote:
And it will be dangerous and fool-hardy if you DO NOT always:
- keep a landing spot in easy reach, and
- never engage power until the landing is planned in you're in position.

Agreed, of course! But the whole point of a "turbo" is to be able to regain altitude :-) If FES only allowed level flight, then it may expand the area where you'll find the thermal you need, but since you need to keep a landing spot in reach for the exact reasons you pointed out, level flight only would be very limiting.

It could be that the pilot in question used FES regularly during his flights and found himself with battery low towards the end (vs. only using FES once with a fresh battery in case of trouble)? I asked for his contact data to get real facts vs. speculation and I'll report if I'm able to reach him.