The chipset of the 13" can drop power consumption as low as the Air but it has a much larger battery. If it wasn't for the display it could run long.
Notebookcheck reported a min power draw of 2.8W with the display turn all the way down (wifi off). That would result in 25h battery life. But that only happens if the everything is asleep and nothing happens. Normal idle was 8-9 W so about three times that.
If you drop display brightness enough and don't do much 16h is probably possible. But you'd really have to read text for hours in a dark enough environment. If you don't do much, the display is the biggest power source by far.
It is basically the same CPU that is in the Air, that Intel wants to sell for tablets, just with a higher max TDP. If you use it for 1h under full load, you will be at around 40% battery life left. Put some load to it and it is dry in no time.