It didn't come with a manual or instructions? I couldn't find them on innokin's site. The cool fire 1 does have reverse battery protection, however. I'm guessing if you do it wrong, it will either let you know, or just won't fire up till you put it in correctly.
A video I saw shows it positive in first towards the top, negative at the open bottom, where you screw on the negative end cap.
Amazing that this important element isn't more clearly indicated.
Enjoy, LeeLee