Petzl do a battery-pack insert for about a fiver that allows AA batteries to be used instead of the big flat one. Obviously then recheargeables can be used, but they only run at 1.25 instead of 1.5, so you end up with 3.75, which is considerably dimmer than three fresh Duracells. The big flat ones are heavy, but in mitigation, they do last for ages.
I'm still considering upgrading my old Zoom with one of these to use as a back-up light as they do seem the business. I've already got an LED in it that I got from Biff ages ago at HE, but that's just a screw-in bulb replacement and is nowhere near as bright as these new ones.