I just pushed the button flat and that was that.
My guess is there develops some heat inside with any battery brand. Perhaps
a chemical reaction, maybe from the bulb, etc.
I have several Battery brands, Sanyo, Duracell, Evnergizer, Eneloop.
I love the Eneloop best because I do not have to worry about make sure I rotate my batteries when I go in the draw.
I ride 90-120 minutes and never go to a low power if the batteries were just put in (any brand). If it does go low, I pull over swap em and continue. I always carry Eneloops as my spares