Honestly can't say I've had this issue. No one's complained to me about Blackberry battery life (though we have plenty). iPhone and Android on the other hand...

Things I would look at, what apps have they loaded, how old is the battery, bluetooth/wifi, OS version.

Maybe install Application Resource Manager if it's on 7.1.
Application Resource Monitor now Available for BlackBerry Smartphones with Battery-Saving Benefits «Inside BlackBerry - The Official BlackBerry Blog