If your laptop’s battery is not charging fully even after being plugged in for a long time, you can try the following steps:

1. Check the AC Adapter power cord for any damages and ensure it’s securely connected at both ends.
2. Check your laptop’s BIOS Battery setting, usually found by pressing F2 when the laptop boots up. Choose the settings recommended for your laptop type.
3. Make sure your laptop is not overheating and check if the power management option is configured correctly.
4. Replace the laptop’s battery in case an older battery is being used.
5. In some cases, resetting the BIOS settings to default can help resolve the issue. Make sure to back up and restore any crucial settings.