Patent ID: 7737580

Claim:
An uninterruptible power supply for providing power to a load, the uninterruptible power supply comprising: an input to receive input power; an output to provide output power; a plurality of battery modules that provide backup power; a power circuit coupled to the input, coupled to the plurality of battery modules and coupled to the output to provide power derived from at least one of the input power and the backup power to the output; a controller; a return line coupled to the controller and coupled to each of the plurality of battery modules; and a first sense line coupled to the controller and coupled to each of the plurality of battery modules; wherein each respective battery module of the plurality of battery modules is configured and arranged to simultaneously provide a respective signal on a respective characteristic signal line that is coupled to the first sense line, wherein the controller is configured to determine a numeric quantity of battery modules in the plurality of battery modules based on the respective signals detected by the controller on the first sense line, wherein each respective battery module of the plurality of battery modules includes a resistor coupled between the respective characteristic signal line of the respective battery module and the return line, and wherein the controller detects a voltage across the first sense line and the return line and determines a total capacity of the plurality of battery modules based on the voltage detected.