This exceptionally powerful “20V Max” (18V) 4.0Ah battery with LED battery level indicator offers superior lithium-ion technology, meaning no memory effect, no self-discharge, and always ready to use. The “PWRCORE 20™” system consists of industry-leading advanced battery and charger technology, plus innovative features you won’t find anywhere else, such as our patented “KEEPCOOL™” battery cooling technology, which increases runtime by up to 25% and doubles the battery lifespan. In addition, the patented “ACTIVCELL™” technology ensures maximum performance and optimum battery protection. For ultimate flexibility, the “PWRCORE 20™” batteries and chargers are 100% compatible and interchangeable with all SKIL “PWRCORE 20™” power tools and garden equipment.