Bosch BAT621 18-Volt 5.0Ah Battery Flexible Power System (FPS) - Works with all Bosch 18-Volt Lithium-Ion tools Maximum Run Time - 25% More Run Time (Compared to Bosch 4.0Ah) Unique Cool Pack Design - Advanced heat conductive housing keeps battery cooler, lives up to 2x Longer Integrated Fuel Gauge - For fast and easy charge status Cold Weather Operation - Battery will work down to -4 degrees Fahrenheit