What is the estimated battery consumption when using bulb mode for an exposure about an hour long? I know the best thing is to test it out, but I'm not in position to do that right now.
Camera is Canon EOS 20D, and lens is Sigma 14mm, if matters.
From the Canon Digital Learning Center:
The battery that is supplied with the Canon 20D is the BP-511A, and it has 1390mAh. I believe this is the same battery that is in the EOS 50D that has the specs outlined above. To that degree, you could probably assume similar performance of approximately 2.5hours in Bulb mode(assuming full battery at 73°F). If you need additional time, the battery grip would provide that.