This 9SX on-line double-conversion UPS system maintains perfect output by converting AC input to DC, then reconverting UPS output to fully regulated sine wave AC. Featuring surge suppression, true on-line operation with pure sine wave output and zero transfer time between on-line and battery modes, the 9SX1500 provides the highest level of AC power protection and battery backup for medical, light industrial, automation and other mission-critical IT applications where space is limited, but premium power reliability is essential. The field-replaceable, hot-swappable internal battery modules allow you to work through short power failures and give you enough time to safely save files and shut down your system in case of a prolonged blackout. Exclusive ABM technology increases battery life by 50 percent and closely monitors battery health to provide advanced notice when batteries need replacing. You can also connect up to four external battery modules (9SXEBM48, sold separately) for hours o