Acebeam H30 21700 battery issues

Looking for some tribe insight into a battery (/maybe headlamp) problem…

My BIL handed me his Acebeam H30 and said, “It doesn’t work. Can you fix it?”

I threw a charged 18650 in, and it worked. Woohoo! Tested the in-light recharging function, and it worked. Woohoo! So the light seems fine.

Finally put the voltmeter on the 21700 battery, and got the big 0.0v – in other words, it had tripped its protection. Gave it a 10 second jump from a good battery and measured 2.6v. It’s in the light, charging now. (Red led indicator is on, so I’m guessing it’s working.)

Soooo, to my questions:

Is the Acebeam 21700 battery prone to tripping its protection randomly?
Does the Acebeam H30 run it’s battery down to a point where it trips the protection on the battery?
Am I a jerk to give back a jumpered battery to someone that doesn’t spend too much time thinking about lithium ion? (Should I suggest – or late xmas – a new battery?)

Thanks for your insight!