At least according to the officially listed specs for both devices: the One (M8) for Windows is listed as lasting up to 21 hours of ‘usage time’, while the One (M8) for Android can withstand up to 12 hours. That’s nearly double the dfiference.
When looking at stand-by time, the difference is smaller, but still noticeable: the One (M8) for Windows lasts up to 15.5 days, while the Android version - 12.2 days.
Obviously, the explanation lies in the operating system, and - at least on paper - this seems to confirm that Windows Phone is doing better with battery management than Android. Then, those are the theoretical numbers, and we’re looking forward to seeing some real-world testing (we’ll be putting the phone through its paces in our own battery life test soon!) to see whether the numbers live up to reality.