Canon BP511A 1390mAh Lithium Ion Battery Pack for Select Digital Cameras and Camcorders

This is the exact same battery that comes with the canon 40d. i recommend it if you ever plan on going on location for a shoot so you're not caught on low power in the middle of a shoot

Same as the battery that came with the camera, seems to work well so far. Extra batteries are always good:)

Great Battery. Got it for my Canon 20D. Used for a wedding this past week in North Carolina where I took over 1000 pictures (preceremony, formals and ceremony) before changing it out. Battery meter still showed full charge but I thought it best to change before shooting the reception events.

This battery work good. It give you confident to use more than copy battery.
I do not know what is inside and I do not know how to find a copy battery that have the same quality.
I compare this one with my 2 copies battery. After that, I throw away the copies.
If you do not have time and do not want to take a risk. Just pay more and enjoy.

You'll need a spare battery for your 40D and this one is the real Canon accessory. Allows you to use one battery and have a spare in the camera bag so you can keep on shooting until the dead battery can be recharged.