I had this happen to me once. You might have something running in the background. Try clearing tasks and/or RAM. I was doing something on my phone, put it in my pocket and started having dinner. Few minutes later my pocket felt really hot. The battery drained from 30% to ~15% in maybe an hour. I cleared my tasks and cleared the RAM which seem to have helped.
I've had this happen to me once as well. I tried to send a text and email and for some reason it wasn't sending, so it kept trying to resend in vain. The phone got fairly hot and lost a like 10-15% battery in maybe 30 mins.
oops sorry i keep forgetting this is a US forum lol m8 is short for mate
i use "battery notifier (big text)" and switch off the normal battery percentage in status bar. it puts a nicer percentage in the status bar which changes colour at set percentages and tells u time unplugged, temperature + voltage in notification pull-down