Battery instead of USB?

Awesome_Guy:
How many would there have to be in the pack? Five? Six? Twenty?

Yes, right, twenty.

If we're talking about alkaline AA, AAA, C, D cells (batteries), they're 1.5V each.
NiMH, NiCd are 1.2V or so each.
What to do, which to use, depends on what's to be accomplished.
With a "boost converter" and two AA batteries, you can get a lot of run time (I have.)
Be sure that the battery (external power) is disconnected from the Esplora whenever you have the Esplora connected to the computer.
http://www.ebay.com/itm/121142828799