If you get that much time out of a pair of AAAs, either the light isn't very bright, or you're running the thing until the LEDs are barely glowing.
There's no free lunch. Long run time comes at the expense of brightness. Period. I ride on 50 MPH 2 lane roads with no shoulders in all weather. I'm not willing to ride with a wimpy light in the dark in a heavy fog with people approaching me from behind at 55 MPH.
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Work: the 8 hours that separates bike rides.