I used to cover long events with my DSLR - on a single charge, I could do two back-to-back 12-hour events, taking hundreds of images at each with the camera on

I used to cover long events with my DSLR - on a single charge, I could do two back-to-back 12-hour events, taking hundreds of images at each with the camera on the entire time, and still have some charge in reserve. Five hours isn't a lot by comparison.