So I've been monitoring battery life using the built in reporting and manual observations and these are my findings. TL;DR: Windows 8.1 consistently gave me 8 hours of real world use. Windows 10 gives me 6.5 hours. That's a major drop, all things being equal. The long version: Windows 8.1 (factory image with my standard install of apps mentioned below) gave me around 8 hours of use. Windows 10 - initially upgraded over 8.1 and all was fine, averaged around 6.5 hours. Decided to clean install, using the Win 10 image using a USB flash drive, same story. Jumped onto Fast track insider builds, same story. Reverted back to 8.1 using recovery image and kept things stock (no apps, clean image). Things went back to around 8 hours. Then upgraded to 10, and we're back at around 6.5 hours. I have Office 2016 installed, with some minor other software. Nothing otherwise CPU taxing (wunderlist, drawboard PDF and Power BI toolset - a pretty vanilla productivity setup). For me, Windows 10 is a battery downgrade. Typical brightness level for my use case is 50%. I've disabled some indexing, and disabled real-time windows defender settings. Doesn't seem to help. While I'm loving Windows 10 as an OS, the less than stellar battery performance has been a major disappointment. Not sure what others have observed. Other observations: Edge CPU activity spikes often, and randomly. Flash is disabled System background tasks ("System") while not aggressively nailing the CPU, is definitely seeing a higher average load than on 8.1 Could be linked to new mail, calendar and photos apps - they seem to be polling and updating quite a bit. No Cortana In use (my language pack and region are not supported) Fan on AC power and battery comes on often. On 8.1 hardly ever. Seem to be related to system processes. Windows shows OneNote and Edge as the top 2 battery using apps. Don't use them any more than I would have with OneNote / Explorer 11 under 8.1. Guess we're all still beta testers even with the RTM image. If MS are trying to get us to upgrade to the Surface Pro 4, they're doing a fine job (and I mean it, please give me back my all day battery life).