Something's wrong with my diamond!!

[Calico_NC]

I Have A HTC Diamond Stock Rom (CDMA) But the problem is my battery is pathetic..it only last barely over an hour at the most if i'm continually talking! And when it goes dead, i cant charge it and talk on it at the same time or send texts as it's not enough power to run..it basically just drains slower than normal instead of gaining.. It takes well over four hours to charge completely, and even then its dead after an hour or so of talking! I keep the backlight on the lowest settings...and i keep my bluetooth off. About 6-7months ago i got a new replacement phone, but they made me keep the original battery i had from my defective phone, so I dont know if its the battery or the actual phone. So what next?? Can Sprint give me a new battery for free ??Or should i get a whole new phone?? Would a new battery solve my problem??? I Just know that somethings not right here!!