iPhone 5s got heat and caused mysterious dent

You dropped it. Heat does not make metal contract. It makes it expand. That's basic physics. It's entirely it's overheating because of damage to internal components that was caused by dropping it.

Well, it didn't spontaneously dent itself.

I too have the same problem

That type of dent takes external force. The phone was dropped or had something exert pressure on the phone. The plastic case may have deformed and then when the pressure was removed restored to its original shape. Plastic does have some ability to deform and not be damaged. Having a case is no quarantee that damage will not occur as you have plainly found out. In fact corners are the most vulnerable to dents as any pressure from external force or drop is concentrated in a very small area. You will have to pay for an out of warranty replacement.

I too have same dent at same place. I think it's due to overheating of battery

A swelling battery would cause it to bulge, not dent.

Brooksphillipjack87 wrote:

I too have same dent at same place. I think it's due to overheating of battery

Please see the Kilted Tim's capsule physics lesson above. iPhones are pretty nifty but they don't violate the laws of physics.