This is a cap designed to fit over the XT60 connector. I usually keep all my Lipo batteries together in a box and it has always been in the back of my head that one fateful day two batteries will short themselves together. Hence, a simple cap.
I've also attached a pattern of 2 and pattern of 6 for those who want to let print multiple parts.
Update: Now with better grip so it would be easier to remove the cap.