Q:  What is a protected button-top battery?

A:  It is the original flat top 18650 cell with an added button top AND PCB (protection circuit board) by a third party manufacturer.  The protected button-top cell is longer than a standard flat top 18650 battery.  The PCB offers protection from over charge, over discharge, over current, and short circuit.  The protected button-top cell has an additional outer wrapper and insulator which must not to be removed.