This is a Genuine Milwaukee M18B5 18V 5.0Ah Lithium-Ion Battery REF6. It is compatible with various Milwaukee power tools and features a long-lasting Lithium-Ion technology for reliable and efficient performance. With a battery capacity of 5 Ah and a voltage of 18 V, this battery is perfect for powering your tools for an extended period of time. It is also designed to be compact and lightweight, making it easy to carry around your workspace.