This HERCULES™ 20V 4.0 Ah Extreme Performance Lithium-Ion Compact Battery uses 21700 battery cell technology for more power and runtime in a compact size. Extreme Performance technology ensures that this battery is optimized for high-demand tools in order to power through some of the toughest jobs. Get up to 40% more power*, 65% more runtime** and 95% more cuts per charge*** than the standard Hercules 2.5Ah pack. The easy-view fuel gauge tells exactly how much power remains before you need to recharge.