Among my brighter AA-powered LED lights, I like this one. 3-watt LED, 2 x AA, ~2 hour run-time, sturdy construction, at $40 won't put huge drain on your pocketbook.

I'll add my vote to the earlier comments about the pre-Gerber CMG Infinity Ultra as a back-up light: simple, sturdy, dependable, runs forever on one AA.

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"Things that have never happened before happen all the time." — Scott Sagan, The Limits of Safety