I have a Canon EOS Rebel 35mm film camera for my photography class and I need a battery, it didn't come with one. What battery do I need to buy?
Find the exact model here, and look for the specifications: http://www.canon.com/camera-museum/camera/film/series_eos.html
Note that there are many different models that are called "Canon EOS Rebel something", and some of them use different kinds of batteries. For example, EOS Rebel XS seems to use CR123A batteries while EOS Rebel 2000 uses CR2 batteries (both of these models are 35mm film cameras).