Hi
joaquimpato@googlemail.comThank you for your asking. Kindly try some stay-at-home troubleshooting tips below:
1. Please check the battery usage of each app. Setting>Battery>3 dots on the top"Show app usage"
2. Enter "Safe Mode" and leave a 100%-charged phone in sleep(idle) mode in a night, if the battery works well in "Safe Mode", please check on any disturbance from the installed 3rd party Apps.
# How to enter and exit "Safe Mode"
https://www.asus.com/support/FAQ/1005163/Is there any zone heating up while using/idling? How long has the battery been used? After using a battery for some time, under some conditions it will have a degree of swelling. This behavior will not create safety issues. However, please contact with the local repair center for battery checking/replacement.
For more information, please refer to the links below
[Phone/Pad] Tips for battery charging and storage | Official Support | ASUS Global[ZenFone/Pad] Power saving skills | Official Support | ASUS Global