I don’t own the tablet so don’t quote me on this but I think the battery life in Windows 10 should be as good as the Hi10’s battery life which is roughly 7 hours at 50% brightness if not slightly better and seeing the recent review Chris posted on YouTube on the Hi12’s in Android, give or take Chuwi’s has done a great job with battery life in Android on the Hi12; the HiBook should be able to get roughly 6.5 hours in Android with 50% brightness and again if not slightly better.
When Chris posts a review of the HiBook on both Android and Windows will get a real life confirmation of how long the battery lasts for this tablet but for the time being I don’t see how the HiBook’s battery life can be any worst than the Hi10’s battery life, so roughly 7 hours on 50% brightness in Window 10 is your answer for now.