Bosch SKC181-303L 18-Volt Lithium-Ion Starter Kit with (1) 2.0Ah Battery and (1) 4.0Ah Battery, Charger and L-BOXX-3 Battery pack design protects the battery and tool; resulting in optimal battery life and performance and 35-Percent more run time Optimized cold weather performance, down to -4 degrees Farenheit/-20 degrees Celcius Cool Pack Technology - Innovative pack design dissipates heat for 2x recharge life Electronic cell protection - prevents cells from overheating, overloading and deep discharging Battery fuel gauge takes the guesswork out of when you need to charge