Hi carleast,
Thank you for reaching Microsoft Community.
Hibernate state still uses power but lesser compared when the device is in Sleep state (see:Shut down, sleep, or hibernate your PC (microsoft.com)). For the Surface Pro 8 battery life: Up to 16 hours of battery life based on typical Surface device usage. Testing conducted by Microsoft in August 2021 using preproduction software and preproduction Intel® 11th Gen Core™ i5-1135G7, 256GB, 8GB RAM device. 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 utilizing 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. Wi-Fi was connected to a network. Tested with Windows Version 11.0.22000.9 (21H2). Battery life varies significantly with settings, usage and other factors. (Surface Pro 8 – The most powerful Pro – Microsoft Surface)
Surface has designed this generation of devices to be up to twice as fast with a balance of performance, battery life, and great user experiences in a thin and light design. As a result of increased performance, overall battery life has been impacted, but we expect customers will continue to get a full day of use from their Surface, and faster charging when they need it.
Kindly try first running these steps below then observe if the battery life of the device improves:
1: Run Surface Diagnostic Toolkit
See: Fix common Surface problems using the Surface Diagnostic Toolkit (microsoft.com)
2: Check for Windows Update
Go to Windows Settings > Update & Security and select Check for updates
Make sure all updates need are installed including Optional updates
3: Update drivers and firmware
Check what is the current OS Build of your Windows version by going to Settings > System > About.
Go to Download driver and firmware for Surface, choose Surface Pro
Then click the link next to Surface Pro 8 then click Download on the next page.
Choose the .msi file that matches your current OS Build and click Next.
After downloading, run and install the .msi then Restart.
4: Run System File Checker Tool
See: Using System File Checker in Windows (microsoft.com)
You may also see this page for details and tips in caring for the battery of your Surface: Caring for your Surface battery (microsoft.com).
Kind regards,
Marrion