How is the battery life on the Surface book/pro? All I about it sounds pretty horrible. Especially compared to the 2011 X220s I use all the time, which have 15+

How is the battery life on the Surface book/pro? All I about it sounds pretty horrible. Especially compared to the 2011 X220s I use all the time, which have 15+ hours I wonder what people really get from these MS things. I don't really care about the OS, but the last Macbook Pro's I bought had crap battery life; the best was the Air 11 inch for me but they don't make that anymore...