No idea how long it will last but the output is phenomenal. Buils quality is pretty good for the price. My favourite flashlight is the Larry light for lighting up a wide area. Totally different from this one.
If somehow there was a way to make a more robust and accurate unit this size I would pay more for it. As it is I have had some mixed results with it. After two pints I blew .07 which seems quite plausible. After a really good party I blew .1 which also seems plausible. But on another occasion I tried it on a friend and it clearly stated he had very little alcohol in him when he told me his consumption was otherwise. Anyway for the money I am impressed that it even lights up. Keep at it BACtrack!!