K810i Battery(New Battery) lasting 7 hours, help?

I've just got a k810i on orange, slight problem, the battery doesnt go for more than 7 hours, its brand new, when I touch the battery, it is really warm, strange thing is the battery drains just as fast when the phones turned off!!
I really dont know what the problem is, I've tried other batteries that work perfect in the k800i, and they have the same issue on this phone, so the battery is ruled out, is it a hardware or firmware problem?