Answer: About 3 hours apparently. See: http://surfaceproartist.com/blog/2015/10/6/microsoft-unveils-surface-pro-4-and-surface-book http://surfaceproartist.com/

Answer: About 3 hours apparently. See: http://surfaceproartist.com/blog/2015/10/6/microsoft-unveils-surface-pro-4-and-surface-book http://surfaceproartist.com/blog/2015/10/6/microsoft-unveils... Battery life of the Surface Pro 4 is 9 hours. The Surface Book will offer 12 when configured as a laptop. But when the Book's display is detached, it will only achieve 3 hours.