Look at your current battery. Let's say it's 700mAH and you get 60 minutes. If you can find a 1400mAH battery you should get 120 minutes.
Got it?
Bob
Ok, I am trying to find an extended battery for my Cannon ZR 500, problem is, is that every website I go to, doesn't tell me how long the battery life is, for example....http://www.atbatt.com/product/5157.asp
I have searched EVERY where for the BP-2L12 info, and nothing tells me its life, as well as any other battery life span.
Can anyone help me find a relatively cheap long lasting battery for the ZR500, I want anywhere from an hour of recording to 2000 if possible, but the best price will definitely be my choice. Also preferably 2 hours of recording, but again, I may just buy two one hours batteries if need be depending on price.

Chowhound
Comic Vine
GameFAQs
GameSpot
Giant Bomb
TechRepublic