I wanted a 2nd battery for my 20D and the Canon BP511A Battery Pack is $103 CDN. Instead I ordered a battery from SterlingTek. The battery is 1800 mA compared to the 1300 of the BP511A so it should last longer...and it's only $11.99 US. It was about $20 with shipping. The shipping was USPS, so there were no extra fees like there would be from UPS, FED-EX etc. I've charged it up and it works fine...I haven't had a chance to see how long it lasts compared to the Canon battery though. From what I have read, the difference is that the cheaper battery is not as well suited to overheating. It does not vent the same as the Canon battery...but it does have overheat shutoff or something like that. It shouldn't be an issue as long as I keep the camera & battery out of direct sunlight for extended periods of time...which I would be doing anyway. I would recommend this for anyone with a Canon Powershot G#, Powershot Pro #, or digital SLR.