Heat is a sign of a problem with software.
I was convinced of that after trouble with a phone. Factory reset and not restore, setup as new and had to ... carefully... install apps.
Of course u was sure it was hardware, cable, piwer adapter. Even bought a 2nd identical phone, Blackberry DTEK60.
Convinced me how software can be culprit. Temperature was hitting 44°C was draining very fast. Usually could leave it alone for days and be safe in a draw as backup. Except it hit zero overnight.
Not every app is tested against every other, every user's phone is unique. All it takes sometimes is one mischievous.