Built-in fan circulates air through the battery during the charging process to cool the battery for faster charge time The Makita DC18RD twin 18v Li-ion charger, charges 2 Makita 18 volt LXT lithium-ion batteries simultaneously. The rapid charge technology selects the optimum voltage and current and temperature is controlled by the forced air system that circulates air through the battery to prevent overheating. and a full charge sound alert confirms when the charge cycle is complete. MAKITA DC18RD FEATURES Makita LXT® is the world’s largest cordless tool system powered by 18V Lithium-Ion slide-style batteries. At the heart of the LXT® System is the 18V LXT® Lithium-Ion battery and the efficient Rapid Optimum Charger. The 18V Lithium-Ion Dual Port Rapid Optimum Charger (DC18RD) charges two batteries at the same time, giving tool users unparalleled charging efficiency so their batteries spend more time working and less time sitting on the charger.