I have an L2D Premium Q5 and it certainly does die without warning. I didn't notice any flickering or anything, it just seems to crap out. Like 10 Wheels said, put some old batteries in there and see what happens. It will turn on and be really dim then get bright for a second or randomly switch to other settings and do other funky things. The first time it happened I thought it was broken, but fresh batteries brought it back to normal.

I've almost had a couple of hairy experiences on dark, rainy nights due to running out of battery juice, but fortunately I was able to swap the batteries with the ones in my secondary headlight (Blackburn Quadrant).