There are 3 way to understand that battery is low.
1)Red indicator in buttons.
2)Dramatic decrease of lihgt compere to beginning level.
3)Manual battery check (3click from off)

But yes if you use it a lot you may forgot about headlamp at all, and then it can turn off suddenly. But I think it is better than annoying blinks as many others headlamps.

The light turns off at 2.75V so it has protection.

And several points I forot to add to review.
1)Current butch of Panda3 has good termal control not just stepdown.
2) Panda3 actualy has stabilisation usual to linear drivers except for hi modes.
3)Panda 3 is compatible with this optics from Ali