M18, Red Lithium XC 4.0 Battery Pack, Extended Capacity, Features Superior Pack Construction, Electronics & Performance To Deliver More Work Per Charge & More Work Over Pack, 4.0A Hours Of Run Time, With Milwaukee Durability Built Into Each Pack, This Battery Runs Cooler & Performs In Climates Below 0 Degrees Fahrenheit/-18 Degrees Celsius, Managed By Milwaukee's Exclusive Redlink Intelligence, Battery Features Overload Protection To Prevent You From Damaging Your Cordless Power Tools In Heavy Duty Situations, While The Discharge Protection Prevents Cell Damage, Temperature Management System & Individual Cell Monitoring Help Maximize Battery Life.