The duration of the battery before it needs recharging depends on numerous factors. See Maximum Battery Life - BlackBerryFAQ
and note that how you use the battery can be a significant factor. The age of the battery is a factor, signal strength, your useage patterns, on and on.
About applications, if you haven't done so already, check and find any third-party applications that are set to run in the background when closed. Fully exit all applications when not being used.
And when you buy replacement batteries, buy either genuine BlackBerry batteries or well-regarded aftermarket extended life batteries and not the cheapest battery you can find. That doesn't mean you need to pay full retail, either. Posted via BlackBerryForums.com Mobile