The Streamlight Strion Piggyback Charger doubles your runtime by charging a spare battery simultaneously so you can keep on working. It includes an integrated micro-USB interface so you can charge using contemporary USB method or with traditional AC or DC chargers. The Strion Piggyback Charger simultaneously charges a Strion flashlight and second battery. It works with all Strion models and uses a USB charger or traditional AC DC charger. The spare battery sold is separately.