Battery Life in Cold Weather

Hi all,

I did a test with my D800 to test the battery life, I plan to shoot some lengthy interval shots at night in the future.

In the comfort and more more importantly warmth of my home, I was successfully able to shoot 500 RAW images with a 25 second exposure and a 1 second interval. My question is how much can I expect the battery life to deteriorate in cold conditions, say -2C for example?

Thanks