People forget that background tasks CAN suck up a fair bit of CPU power, and that in turn leads to the battery running down faster. Now, I don't know how things are on the Blackberry in terms of what is turned on/off by default, but if you turn off GPS, WiFi, Bluetooth, and whatever you are not using at that moment, it WILL save you a fair bit over the course of a day. Press and hold the "home" button to get to the task switcher and close the apps you are not using. Many people forget how much is running at any given time if you don't pay attention to it.
I made a point of "conditioning" my battery when I first got my phone. The idea is to calibrate the battery and phone to get the best amount of life. You can read up about "conditioning" a battery, but the short version is to charge to full, and then let it go for an extra two times, then use the phone fully to drain the battery ALL THE WAY DOWN until it is forced to shut down. Then charge back to full. Five full cycles of full+2 hours, then down to ZERO will get the most battery life for you going forward.
As others have said, going from a phone with a TINY screen to one with a large screen does mean that there will be shorter battery life. Adjust your screen brightness down a bit, keep running apps to what you are actually going to be using, etc. Power Saving mode will also help. I did a test with my S3 when I first got it where I streamed Bluetooth audio to my car for 2 hours worth, didn't play games but did some browsing, worked for four hours(where I wasn't using my phone at all since I was working), and I had to push to get it down to zero. It ended up being 13 hours or so worth of battery. Playing games obviously will drain the battery faster.
Moderate use like that, where you are too busy doing other things to be worried about your phone during the work day will do the job. If you don't use a bluetooth headset all day long, then why keep bluetooth on all day? Or WiFi, if you are not able to use WiFi most of the day, turn it off.