M18™ REDLITHIUM™ batteries are compatible with all MILWAUKEE® M18™ cordless tools. The REDLITHIUM™ XC4.0 battery delivers 4 Ah of run time - even in sub-zero temperatures. Milwaukee REDLINK PLUS™ intelligence prevents overloads and protects against cell-damaging discharge. Revolutionary cell monitoring and temperature regulation prolong the operation and life expectancy of the battery for fewer work interruptions and more recharges than ever. The Milwaukee Multi-Voltage Charger is compatible with all M12™ and M18™ batteries. This unit charges batteries sequentially, reducing the user.s time managing charge cycles and communicates directly with the battery pack to monitor cell voltage, temperature and charge status to ensure a full charge. Buy one, receive one free good with this exclusive pack that includes two M18™ REDLITHIUM™ 4.0AH Batteries, an M12™ & M18™ Multi-Voltage Charger, and a contractor bag. Features: Built-in charge meter on battery; Battery resists drainage when not in use; Battery rechargeable in 60 minutes or less; Battery compatible with all Milwaukee M18 tools and chargers; Battery Fuel Gauge displays remaining run-time; Charge management: Charger communicates with the battery pack to ensure a full charge and battery protection; Single unit simplicity: Charges M12™ RED LITHIUM™ and M12™ Lithium-Ion batteries