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:
For long exposures, camera makers rate the battery power in terms of total length of time a freshly-charged battery can hold the shutter open. Here are a few examples supplied by Canon’s engineers, at 73°F/23°C:
EOS Rebel T1i, Rebel XSi, Rebel XS: Approx. 2 hours EOS 50D: Approx. 2.5 hours EOS 5D Mark II: Approx. 4.5 hours
Most Canon EOS digital SLRs accept an optional Battery Grip, which does allow the photographer to install one or two rechargeable batteries. With two batteries installed, any of the above figures would be doubled. Battery grips with an extra battery pack can be a great accessory for extensive shooting of fireworks displays.
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.