My Aspire3 modelN23C3 battery suddenly will not charge greater than 80%

@CarlP

If your Acer Aspire battery suddenly stops charging beyond 80%, it's likely a battery health management feature or a software issue, rather than a hardware problem.

Check for Battery Health Management Settings:
If you have the Acer Care Center app, check for a battery health management setting that limits charging to 80% to extend battery life
Thee, in Windows settings, search for "Battery" and check for any battery optimization or charging limits that might be set.

Try Calibrating the Battery: Deep Discharge: Run the battery down to almost zero (but don't let it completely drain) and then charge it back to 100%.

If the issue persist generate a battery test report
To get a battery test report on your Acer laptop, open Command Prompt as administrator, type powercfg /batteryreport, and press Enter. The report will be saved as an HTML file, which you can then open in your web browser to review your battery usage and health.
Also, try to uninstall and reinstall Battery Drivers:
In Device Manager, uninstall the battery drivers and then reboot your computer. Windows will automatically reinstall them.

If the battery is old, it might be losing capacity and not charging to 100% even if the software settings are correct.

@CarlP

Try a power reset.

To reset your Acer laptop using the battery reset pinhole, first ensure the laptop is turned off and unplugged from the AC adapter. Locate the battery reset pinhole on the bottom of your laptop, usually marked with a battery icon. Using a small paperclip or a similar object, press and hold the reset button inside the pinhole for about 5 seconds. After releasing the button, wait for approximately 5 minutes before plugging in the AC adapter and powering on your laptop. This process temporarily disconnects and reconnects the internal battery, which can help resolve power and battery-related issues.

in few Aspire models the  Acer Care Center App has settings to Turn Off/On the Battery Charge Limit. Did you try reinstalling the battery drivers in device manager?