Extra Smart Series (Tower) 650VA~4000VA General Features: * Smart backup time estimation * Adjustable voltage sensitivity, voltage-transfer points, & charging voltage. * Generator compatible * Automatic restart of load after UPS shutdown * Smart AVR function (Two buck / boost modes) * Cold-start capable * Audible alarm * Hot-swappable batteries (optional for 3K & 4K models) * Network manageable (SNMP optional) * Full function of LCD display (LED display optional) * Smart battery management * Intelligent double stages of charging control