Blackberry pearl newer one with video, I have a question about the battery? How

[Pink22]

long should it last? I got a new blackberry for cricket service from the store. I charged it correctly and fully and then after two hours of barely texting, the battery completely died. I went and got a new one no problem. NOW i have a new one and charged it correctly again. Its been on since 12:30 and by 3:00 it has half the batterly left. I have only texted probably twenty texts at the most. What is going on? the guy from the store said it could be the phone? Is this normal? I havent been web surfing or anything at all. How long should the battery last or whats going on? thank you