The Peax M36 18650 3.7V Lithium-ion Rechargeable Battery has a High Performance 3600mAh Capacity Featuring a Flat Top to Prevent Overcharging, Short Circuiting and Includes Discharge Protection.  It's the Perfect Companion to the Backcountry DUO Headlamp.

*One battery is included with the Backcountry Duo Headlamp.