Milwaukee M12B4 12v 4.0ah Red Lithium Ion Battery Up to 2 x more run time, 20% more power and up to 2 x more recharges. Uses the sophisticated Milwaukee REDLINK Intelligence - provides optimized performance and overload protection using total system communication between tool, battery and charger. The most advanced system in cordless electronics. With overload protection means the user is prevented from damaging their cordless power tool. The temperature management system and individual cell monitoring keeps the battery in the ideal temperature range to provide maximum life. Runs 20% colder than other lithium-ion technologies. Durable construction rubber over mould, rigid metal cage and 3 layers of shock absorbers help protect the battery. Also features an on board fuel gauge to help monitor the charge. Up to 2 x more run time, 20% more power up to 2 x more recharges.