ARB-L18-3500U is a high capacity 18650 Li-ion rechargeable battery with a built-in micro-USB charging port. It also includes a protection circuit in the anode to help prevent short circuits, over charge/discharge and over heating. This battery can quickly be charged without the need for a separate charger. This not only save you money from purchasing a charger, but also convenience of not having to carry around another device. This will work in all of the models that utilize the standard Li-ion 18650, including best sellers like the PD35, PD35Tac, TK20R, TK75, TK15UE, etc.