Don’t comment without owning the phone. It does have a battery.not water? How will it drain? It is best phone, no issues at all. Those who post issues are liars who are trolls. What if it heats? Use it to iron your clothes and keep yourself warm.
After all it is winter. Did you flash custom ROM, use cyanogenmod and miui to root the phone. Miui is in Chinese and Kannada guys may not know it, so use Hong Kong ROM in English. Wat are you talking about! If it does not help buy extra batteries from mi.com. practice hypnosis because if it drains you’ll not notice it.