So here's the deal, I'm going on vacation in the near future and will be shooting a lot of video on my Canon HV20. I've seen many things, but am curious to know what extra batteries I should purchase. I've seen some advertise 4 Hrs! but canon's only lasts 1... would this 4 hr battery exist, it seems a little strange to go through 4 tapes on one battery before it dies... Advice?