Many people do not consider the battery. I fly high powered RC helicopters and planes with similar lipo batteries to the technology used in cell phones. Once in a while, a cell (battery) will go bad. One test you could do is to remove the battery from your phone and another identical phone, and do a discharge test to measure how many milliamps are consumed before the two batteries reach discharge voltage of 3.7 volts. Be sure to charge both batteries to full charge at 4.2 volts first. Now, this is very impractical for most phones with sealed batteries, but my point is that your battery could have high resistance (an indicator that it is defective or going bad) which would result in reduced capacity. It would also explain why your phone always feels warm because lipo batteries with higher than normal resistance will heat up more during use. You could also just try having your battery replaced by a service center and see if that solves your problem.
