I just read this discovery (it was new to me anyway!) that Ronen posted over at BerryReview. It turns out that OS4.5 does a better job of managing the way battery life is displayed on your BlackBerry.
Think back to your BB usage... have you ever had a time where your battery indicator shows some juice left, but the device has decided that the Battery is too low for radio use?? I know it's happened to me dozens of times. But it seems with OS4.5 you can run the device with the radio on right to 0% remaining. Only at 0% does it kill the radio, and even then the device will still function as you seek out an outlet to recharge! AWESOME improvement.