Since we are not sure what OS you are running its a moot point but if you are running any of the 7.1 OS's, you already have a free battery anaylizer that boldkeyboardholic referred to. If on 7.1 go to:
Blackberry Device Anaylizer
...and click on "Draining too quick" or what ever the option is (can't remember). Once it's set up, give it a day and it will tell you exactly what your discharge rate per hour is; the average charge rate and average level. Run it for a couple of weeks to give you a better idea.
It shows a graph of your phones discharge rate and then when you click on details, it no only shows the above, but it also shows number of emails sent per hour/texts per hour, etc. Excellent Analizer as is all of the new Free Tools on this handy little application. Give it a try first-----and if you aren't on 7.1, do yourself a favor and upgrade to it. Light Years ahead of 7.0! Good luck!