Our experience with a new fully-charged BlackBerry is that iHeartRadio drains the battery at about the same speed as making a phone call.
If you get 2 hours of talk time, you should have 2 hours of listen time. We recommend having your BlackBerry charged to ensure adequate battery life when listening to iHeartRadio for long period of time. Individual experience will vary based on prior charging patterns and the age of your battery.