Oregon PowerNow B500S 40 Volt Max Standard 1.25 Ah Lithium-Ion Battery Pack 40V MAX Lithium Ion: High capacity cells provide no-fade power and long run time. Lithium ion batteries combine high power with light weight. Lithium ion batteries delivery constant power up until complete discharge No memory effect: Charge maintenance and full discharge is NOT necessary to retain consistent capacity throughout the life of the battery. Fully charged battery voltage measured without a workload is 40 volts. Nominal voltage is 37.