The Vertiv Liebert APS Battery Module Kit (APSBATMODCU) consists of a pair of APS Battery Modules for replacement or runtime expansion of the Vertiv Liebert APS UPS. The battery modules may be added or replaced online with no interruption or danger to the connected equipment if the UPS is not operating on battery. The Liebert Battery Module Kit is user replaceable and hot-swappable. Its simplified setup allows easy installation. It is fault tolerant so you can add and remove module without disruptions in power. When AC utility fails, the battery module supplies power to the load. Two battery modules are connected in series to form a battery string. Each battery module has monitoring and controls that isolate the battery module in the event of a battery failure. The battery strings are connected in parallel to provide back-up time and/or redundancy.