The Makita BTW251 is a Lithium-Ion 18-Volt Cordless Impact Wrench Kit. It features 4-pole maximum torque motor which delivers 170 ft-lbs of efficient torque in a compact size. It has ergonomic shape which fits like a glove with even pressure and easy control. The BTW251's Lithium-Ion battery provides longer run time, 5x lower self-discharge (for use any time) & 16 firm holding contact terminals (for constant high power). The Makita BTW251's rapid optimum charger and battery communicates throughout the charging process using the built-in chip in the battery and built-in CPU chip in the charger. The BTW251's charger also uses Active 3 Control for current control, thermal control & voltage control.