I use a XPAL 18000 battery http://www.youtube.com/watch?v=rNhPGcnOfkk for days upon days use and a smaller version that gives me an extra 4 hours on my Android smartphone and Iphone this also gives me apps like Endomondo, Track Me Micoach etc to record the routes and also have a Zepyr HXM HRM plus Google maps Sat Nav now that it supports Cycle routes. this video was when i used to have a standard Sat Nav and BB but still went upto 5 days use