I just did a 4 hour test, letting one of the grand kids play with it in the pool, 86°, water temp, light was used during 3 hours of diving prior to this test without charging.
mine doesn’t turn off until the batteries are highly discharged. If you have some known good batteries maybe give those a try, mine are pretty good but just one weak cell will cut burn time a lot.
I’ll take them off your hands for further testing if you like.
I agree that the type of diving you do is nothing like anything I do so mechanical function is all I can test.