There's a 23 Wh battery inside (some sites refer to a bigger battery
capacity but I think that's for the non-Pro version of this tablet that doesn't have the projector) and my colleagues at Notebookcheck got over 9 hours in their WiFi surfing test (150
nits brightness.)
[24] Tested by HP using continuous video playback, 150
nits brightness, system audio level at 50 %, player audio level at 100 %, played using a Full HD 1080p video stored locally, headphone attached, wireless off, auto dimming off, Actual battery life will vary depending on configuration and maximum
capacity will naturally decrease with time and usage.