An uninterruptible power supply (UPS) system that may incorporate a battery subsystem including at least one battery for generating electrical power, and a UPS subsystem including at least one power module. At least one first bus system may couple the battery subsystem to the UPS subsystem to supply electrical power to the UPS subsystem. An input and output (I/O) subsystem is in communication with an output of the UPS subsystem for generating an output signal. At least one second bus system may be used for coupling the output of the UPS subsystem to the I/O subsystem. At least one of the first and second bus systems may include a pair of parallel coupled, independent busses, and may further have a tie bar for enabling the pair of busses to be reconfigured as a single bus.