myPhone problem.

Hey there fellow iPhoniers. I'm new to this Mac-forums, and I need your help.
I have several problems with my iPhone 3g [8gig] and you professionals could probably solve my nightmares with a single, simple inhale.

Oh and thanks for taking your time for me.

1. I went in school, with full battery life. My iPhone was on sleep mode. I turn it on in 2-3 hours.

( Homeroom => 4th Period ) and the battery life was at around 25-35%.

Why is this happening and how can I fix this?

 

Sorry, I should've specified before, I don't know any iPhone terms, ie : Jailbroken, FW.

But it's on Push.

Another Question : I read a topic the other day about, Pandora running without actually being on the application. It said to download "Backgrounder", but I assumed that it had to had to be "Jailbroken."

So , I ask what happens when it's Jailbroken, Pros, Cons, etc.

Thanks