Well done Canon for leaving you free to choose. If their battery pack uses LiOn batteries it'll last longer between charges. But regular NiMh batteries (Energiser, Duracell) are cheap, recharge quickly and have good life.
Best of all if you're out and about you can drop in regular non-rechargeable batteries available virtually anywhere -- though obviously stick with the premium versions.
Just purchased Canon powershot sx20 is. It takes 4 aa batteries, which it seems to burn thru very quickly.
I plan on getting rechargeable Ni battery set. Canon says to use their battery kit.
The question is there a difference in batteries or will I get the same performance from any Ni rechargeable ?