Is there something wrong with my iphone battery?

[lovlykayla]

I recently bought a used iphone off ebay. It is about 12 months old. I am just wondering my iphone usage is a little over 2 hours and my standby is 7 hours. And my battery life is around 33% at about 6.00. I fully charged it the night before and it was full battery in the morning. Would i need to change my iphone battery or is this normal?

[hchavarria]

Wirelessly posted (Mozilla/5.0 (iPhone; U; CPU iPhone OS 3_0_1 like Mac OS X; en-us) AppleWebKit/528.18 (KHTML, like Gecko) Version/4.0 Mobile/7A400 Safari/528.16)

This depends on usage because on my 3GS on heavy email days by 6 my phone is dead.