The Makita BL1850 5.0ah 18v li-ion battery offers superior performance with its optimum charging system, outperforming previous models like the BL1830 and BL1840. This twin pack contains two 5.0ah batteries. LXT Lithium-Ion technology combined with an optimum charging system provides 280 percent total lifetime work and doubles the number of charge cycles. With 5x lower self-discharge, the battery cells remain active and ready for use, even after extended storage periods. Charging at any time has no adverse effect on the battery. Built-in shock-absorbing features protect the battery, and sixteen firm holding contact terminals minimize power loss or fluctuation in high-vibration work environments. The integrated Memory Chip communicates with the charger to maximize battery life through 3 Active Controls (Current, Voltage, Thermal). This battery is compatible with all Makita 18-volt LXT li-ion machines. Makita's STAR Protection Computer Controls protect against overloading, over-discharging, and overheating by enabling real-time data exchange between the tool and battery. For high-drain applications, Makita tools and batteries are engineered for industrial use. STAR Protection allows the battery and tool to communicate and cut power during abnormally high current draw, protecting both. Lithium-ion batteries are designed for sustained performance, but completely draining the battery can cause damage.