Patent ID: 7763993

Claim:
A direct current (DC) uninterruptible power supply (UPS) having an auto-ranging backup voltage capability, comprising: at least one input; at least one rectifier connected to the at least one input; a common node connected to the at least one rectifier; at least one DC output connected to the common node, the at least one DC output adapted for connection to at least one electrical load; and an auto-ranging battery backup circuit connected to the common node, comprising: negative and positive terminals, first and second diodes connected to the negative terminal, a first string of batteries connected to the first diode, a second string of batteries connected to the second diode, a switch connected between the first string of batteries and the second string of batteries, a third diode connected between the first string of batteries and the positive terminal, and a fourth diode connected between the second string of batteries and the positive terminal, wherein the switch places the first and second strings of batteries in parallel when opened, and places the first and second strings of batteries in series when closed.