There are several reasons why a phone battery might overheat. Sometimes, it is an isolated incident, while others have a fundamental flaw.
There are two main causes of lithium-ion batteries going wrong. The first is when one gets wounded, for instance, in a break or piercing. This could be caused when you drop your phone, which might make the battery short-circuit, causing it to expand and sometimes explode.
Heat is the other main cause of battery fire and is usually related to charging. Charging a battery will result in some heat generation, and if the temperature gets too high then an internal short-circuit can occur, it is not always because the battery itself is faulty.
Here is a guide to help prevent your battery from overheating and your device catching fire:
• Use the correct charger – Ideally, use the supplied charger with your device.
• Unplug once charged – Try and be aware of when your phone is fully charged and unplug it to avoid unnecessary heat build-up
• Charge in a safe place – it might sound silly but don’t leave your phone charging under your pillow all night, for example.
• Remove cases – a case is like putting a jacket on and will restrict heat dissipation so take it off to charge or during other heat-inducing tasks.
• Avoid direct sunlight – your phone won’t get a tan but the sun will heat it up so don’t leave it in places like your car dashboard, especially when charging.
• Let your phone cool – whether you’re charging, gaming or something else, let your phone cool down if it gets hot.
• Avoid pressure – you don’t want the battery to get a puncture so don’t sit on it or allow it to come under excessive pressure.
Source: The Sun
