The 20V/60V MAX FLEXVOLT 9.0 Ah double-voltage battery automatically changes voltage when you change tools, providing up to 6 times the runtime in 20V MAX tools and the power of corded tools in 60V MAX and 120V MAX tools. Tackle tough jobs with this battery, as its patented technology and large-format cells allow it to run at a cooler temperature than the competing 9.0 Ah battery, under constant discharge. This is the battery for FLEXVOLT power and long runtime.