Can't add to the cr2032 discussion, but wanted to defend my Knog! I've got a Knog Blinder 2 which I got from PlanetX during one of their many sales ... and I quite like it. Had it since Feb. Good things: rechargeable, rubber strap thingy works well for me (though it obviously has a life span), very bright for its size - enough light to cycle unlit roads in the dark. Main downsides: as someone else said, beam shape isn't ideal so you need to aim low to avoid dazzling if around other road users, and side visibility is really poor. Not had any problems with water - it's been soaked regularly and has coped fine so far.