billpealer: or a single 14500.. it would fit in a standard single AA batt holder? right?
That might work. I've experimented and my Mk. IV board and determined it would fit inside 1.25" on top of a 7.4V side-by-side 14500 pack (Example Link) but not for the fact that I mounted the ADXL335 on top of the Pro Mini. That's two layers of headers that eat up the clearance and it just baaarely won't fit. However, Canobi's board is flatter because he doesn't piggy-back the ADXL335, so it's one layer thinner than my Mk. IV prototype.
It would be ideal if we could find a side-by-side 3.7v 14500 (or even better, a 14650 pack) with a load-balancing PCB that would output 3+ amps. That way you'd get excellent battery life and still be able to support full three-channel color change. That's pretty specific, though. Might be hard to find. Edit: Found one. Never heard of this supplier before, but at least I know they do exist. (Link)
The problem with using an AA battery holder for the cells is that the battery holder itself also takes up space. It might still fit, though. It's worth looking into.