Average Battery Life is about 4 hours. The product description, (That MOST people seem to ignore), is "UP TO 5 Hours." 5 Hour Battery Life IS NOT Guaranteed. On a FULL charge, battery lasts 4 to 4.5 hours.
note that battery life is specified at minimum backlight ; i ran mine for 5 hr 25 min , then i recharged even tho it was still going. i imagine those who got 4 hr. were using the default backlight setting.