You could probably make popcorn pop with the total power in a cellphone battery (not an actual battery, mind you, just the juice that's in it). You'd need all of it, and you'd have to discharge it all as microwaves, but it might work. Dumping the entire battery of my treo in one minute would give about 400w for that time. This assumes perfect efficiency, which ain't happenin', but 400w delivered right would pop some kernels.