there is a really helpful thread and you should find all the answers there:
http://www.bikeradar.com/forum/viewtopic.php?t=12666507&postdays=0&postorder=asc&start=860&sid=61c81fc534bfda880625e7267be41118saving you from reading thrue all the 44 pages though I can tell what I read there was that people recomended to charge around 2 hours on a wall plug then leave the rest for the computer.
Mine was broken though, it never showed 'battery full' (blue light solid) even though I had it plugget to my computer for over 30 hours and no matter how long I charged it it only got 35 mins of footage before the battery died. Aööen the eBay seller has just prmosed to send me a new one so I'm looking forward to get to play with this one!