You can also buy pre-charged rechargeable AAs and use them right out of the package.

The Fuji HS20 is good for over 1000 pictures on one set of Eneloop batteries. You can find three classes of Eneloops on Amazon.com. The latest, highest capacity Eneloops would give you even more pictures on one set (I believe it was the standard, lower capacity Eneloops that gave 1000+ pictures).

You could also use alkaline or lithium non-rechargeables when or if necessary.

Also, many stores (I've seen them at Staples, Radio Shack, supermarkets, Walmart, Kmart, hardware stores, pharmacies, and elsewhere) now sell the pre-charged rechargeables.

Depending on how much you shoot, you might not have to buy many (or even any) extra sets, especially if you start out with a set of high capacity cells and a camera that is good for so many shots per set.