This PCB protects Lithium Ion batteries configured in 2S from over-charging and over-discharging.
It also protects the cells from over-current loads, limiting the maximum output to 3A.
It also features short-circuit protection, which protects the batteries from damage in the event of a short on the output wires.
This module is NOT a charging circuit!  An adequate charger must be used to properly charge your batteries.