My Windows laptop (Lenovo Ideapad S940) ran out of batter while presumably in the sleep mode in my backpack on multiple occasions. It got so ridiculous that now I listen to its fan after closing the laptop lid to make sure it really really in the sleep mode. I even went as far as trying to figure out how to revert back to the old S3 sleep mode instead of the new Windows 10 "connected standby", but it turned out to be quite a task (and I think it broke something else, so I had to revert things back).