The Wesco 20V 4.0Ah Li-ion Battery Pack, model WS9940, is designed to provide maximum runtime for heavy-duty applications. This lithium-ion battery pack has a capacity of 4.0Ah, ensuring long-lasting power to keep your tools running smoothly. It is compatible with 20V Max lithium-ion cordless tools, offering versatility and convenience for various projects. Additionally, the battery pack is equipped with safety features such as short circuit protection, overcurrent protection, and overcharge & over-discharge protection. With more efficient power management, this battery pack also boasts a longer service life, making it a reliable choice for professionals and DIY enthusiasts alike.