There are enough and more stories about exploding of phones due to overheating. The fact is that even on charging your phone overnight, you can be worry-free. The batteries do emit heat as they are in the charging process. The only thing is to keep in a ventilated area for charging. In fact, modern phones literally stop charging as it reaches 100%.
Thus, if your phone stops at 100% charging, avoid keeping it for prolonged hours. This will degrade the health of the battery. Batteries are complicated, adhere to these guide points:
A charger may turn the juice off as your phone attains 100%. However, if it is on during the night, the charge will top off. Charging it more than required constantly means it leads to higher temperatures and overtime this reduces the capacity.
Avoid waiting for your phone to reach zero % to recharge. Full discharges harm the battery than the partial discharges. Once your phone reaches 35% to 40%, get it charged. This preserves the battery capacity.
Keep your phone cool and you can do this by taking off the phone case while charging. Overnight charging is a matter of concern for people who do not consider buying every year or two a phone. People replacing once in 12 to 24 months need not sweat considering overnight charging. However, if you wish to hang with the same phone for a few years, retain your battery capacity for a longer time. You can do this by resisting the itch of overnight charging.