Bosch SKC181-101 18-Volt Lithium-Ion Starter Kit with (1) 4.0 Ah Battery and Charger Works longer - up to 65% more run time CoolPack Design technology - innovative pack design dissipates heat for 2x recharge life Optimized cold weather performance, down to -4 degrees F / -20 degrees C Integrated battery fuel gauge Electronic Cell Protection (ECP) - prevents cells from overheating, overloading and deep discharging