The Canon NB-5L is a rechargable battery for some of the newer Canon digital cameras. I use this particular one in my Canon SD870 ELPH Point & Shoot camera (which is an excellent camera I might add). This particular camera has a large 3" LCD, so this battery is certainly tested in the stamina department.
With the Canon charger that comes with most cameras, this battery charges fairly quick, in about 2 hours if fully drained. Running around with the camera, if I turn it on only when I'm shooting and don't wastefully drain the battery, I can shoot with it for a few hours. If I were to leave it on continuous, probably 2 hours I'd say. I wouldn't buy an extra Canon brand one unless I could find a great price though, as the other brands sell the same NB-5L type battery at about a third of the price. I myself picked up a DOLICA knock-off for about $15, and thus far it's performing just as well.
Ofcourse, if you can find a good deal on a brand name product, go for it.