I hope I'm not asking for something that's already been posted, but I'm looking for something to power my camera and flash. I've had a couple of gigs that last three - to - four hours, and I'm getting kind of tired of burning my hands while changing aa's on my flash

I have a k20d with grip and a Metz 58 AF-1. I saw a Metz and a third party option (quantum batteries) but was hoping there was something reasonably sized (read: portable) that could power both.
Thanks!!!