There's nothing to check - Microsoft uses the same battery test
"Testing consisted of full battery discharge with a mixture of active use and modern standby. The active use portion consists of (1) a web browsing test accessing 8 popular websites over multiple open tabs, (2) a productivity test utilising Microsoft Word, PowerPoint, Excel and Outlook, and (3) a portion of time with the device in use with idle applications. All settings were default except screen brightness was set to 150nits with Auto-Brightness and Adaptive Colour disabled"
for both SP8 and SP9. It gave 16 hours for SP8 and now gives 15.5 for SP9. No wonder as battery on SP8 is 51.5Wh and on SP9 47.7 Wh. I was really waiting for this announcement and now I'm pretty sure SP8 with discount is a better option. The fact that they moved USB ports to the left is downgrade for me.