Just built this... Cost me two dollars and it works great. I used an 18350 could also have used an 18650. Purchased parts- and ego to 510 adapter. Parts used (I had on hand) plastic battery box. laptop mouse button (fire button). Was bored today!
Notice a person could store two more batteries below the installed battery or one battery upright and a small bottle of juice. Don't throw away your old battery cases!