The usage time remaining statistic is something we all tend to take for granted on our laptops, but it's not something we're accustomed to having on our tablets; at least iOS tablets, that is.
Powerleft is a jailbreak tweak that aims to fix this oversight, adding a usage remaining indicator conveniently in the iPad's status bar. Now you'll be better equipped to know if you can sit through that 3 hour movie, without reaching for the charging cable.