Reviving this thread since it made me think.. Last year the batteries typically lasted what I put above. This year it wasn't even lasting a day. Finally figured out why! Last year put the batteries in the panniers typically wedged with junk around it, the light I have has extensions. This year just had it attached to the stem. I moved it back last weekend and indeed it lasted 3 days this week or all week. Maybe someone needs to come up with a battery insulator!