I have a problem with my iphone 3G. Last Saturday i took it out of my pocket and realized it had little battery remaining and it was very warm. I thought this was unusual but then charged the phone back to full. After charging the phone to full i noticed that after 4 - 5 hours on standby it would be under 20% battery. This had never happened before last Saturday i usually get 2 days of standby time.

I thought it may have been a software issue so i restored the iphone in itunes, i didn't sync my iphone with a backup i just left it as if it came out of a shop, however i now get about 6 hours of standby time.. from it. So i downgraded the software to 3.0 im still getting poor battery life i have also noticed that it is consistently warm like it is doing something in the background. Ive even left it in airplane mode and disabled location, wifi, blue tooth, push everything, turned off 3g. But nothing gives a significant difference is this a hardware issue? Have i broken the battery?

Here is some infromation about my iphone:
Iphone 3G
2 Months old (was a replacement phone from carphone warehouse insurance)
Currently running iphone os 3.0
I have windows 7 professional on my computer.

Thanks for reading, i hope ive put this in the right place and have observed forum rules if i haven't im very sorry.