Just a small warning - I bought a couple of extra batteries for my 5D and 30D (as they take the same type). Canon originals were £45 each and the cheaper ones were £15 !
A year in and I find that the cheaper ones just do not hold their charge anywhere as well as the Canon ones. To the extent that I cannot rely on them - except as real emergency ones.
I don't know if others have had this problem - or maybe it's just me getting an unlucky unit(s).
I go from a full charge to half empty in 10 shots (with 2 batteries in the extended grip unit.
Maybe you gets what you pays for??
"Ilse, a childhood friend of mine, once found a raspberry in the camp and carried it in her pocket all day to present to me that night on a leaf. Imagine a world in which your entire possession is one raspberry and you give it to your friend"