Hi,
Are you sure that there's no advanced settings?
Check the [https://www.online-tech-tips.com/computer-tips/how-to-configure-the-power-options-for-your-laptop/|battery or sleep settings](change to ''do nothing'') and see what happens.
Also try connecting an external monitor to the laptop and check what happens to the display when the charger is disconnected to see if it may be a laptop display panel problem when on battery power only