I have a cygolite hotshot, seems to last FOREVER in blinky mode. It's plenty bright but fairly directional. I probably use mine a few hours a week and charge it monthly when I think about it, so I have no complaints. I think it's supposed to last 4 hours in solid mode, so figure way more than that in blinky mode.

And for just $30, I have a spare that I keep charged and I rotate them in and out. YMMV.