A little trick used by many pilots, these XT60 end caps are a nifty solution to cover the open connections on your XT60 discharge plug on your battery. 

There is a small chance something could work its way into the connector and possibly discharge the current unsafely. The chances of that happening are low, but you never know!

Putting these on charged lipos is also a good way to separate charged from uncharged batteries when sorting through your lipos.