Been riding my all-mountain Rx in the Sierras but one battery is just not cutting it. I've got no problem spending the money on an extra battery but what's really killing me is the powerpack 500 seems to be available everywhere around the world except the good old USA. I can't see spending this much money on a 400 when I can get a 500 for just a few hundred dollars more. I have been checking out European vendors and it appears they can ship me the 500. Is this possible? Has anybody done this?