iPhone 5S draining overnight

I think this problem started after I updated to iOS12.4.9.

When I checked the settings for battery usage, it shows a steadily declining graph from 100 to 0%. The thing is nobody used the phone and the screen on time is only 3m with 0m screen off.

Messages app showed 3m usage with 87%.

The phone also gets warm during charging recently even when it reaches 100%.

This never happens and the iPhone usually lasts a few days without usage. Battery has been replaced before so it’s not the battery.