Battery discharge while in off

Hi about 2 months ago i was charging my phone and placed it into computer's CPU cabin where temperature was high since then my Phone start draining battery too much it taking 5-8 hour to discharge whether i m doing something or not.I if shut it down completely after 8 hour of sleep it can easily drain battery from 50% to empty.i have changed the battery but problem is still there. it also take 4-6 hour to charge.