Hi Ben,
Welcome to Microsoft Community.
I'm Hahn and I'm here to help you with your concern.
I'm sorry to hear that you're having trouble with your Surface book's battery.
The batteries in Surface Book may charge at different rates, depending on the power state of each battery. Whichever battery has less than 20% charge will be charged first. When both batteries are at 20%, the clipboard will charge to 85%, and then both batteries will charge to 100%.
If one battery is fully charged but the other is not charging, you can try the following:
- Force a shutdown and restart your Surface: Force a shutdown and restart your Surface - Microsoft Support
- Run the Surface Diagnostic Toolkit: Fix common Surface problems using the Surface app and Surface Diagnostic Toolkit - Microsoft Support
- Remove and reinstall battery driver:
- From Device Manager, expand the Batteries category.
- Double-tap or double-click Microsoft Surface ACPI-Compliant Control Method Battery, select the Driver tab, and select Uninstall > OK.
Note: For Surface Book devices there will be two battery drivers to uninstall.
- From the Action menu, select Scan for hardware changes.
- Reset using the most appropriate choice. If you've tried basic troubleshooting options, you may need to restore or reset your Surface. If the issue occurs after a reset, then the root cause is very likely hardware related. Restore or reset Surface for Windows - Microsoft Support
I hope this helps. If there is anything not clear, please do not hesitate to let me know.
Your Sincerely
Hahn. W - MSFT | Microsoft Community Support Specialist