A non-transitory computer-readable medium storing sequences of computer-executable instructions for operating an uninterruptible power supply (UPS) system having at least one first input coupled to a primary power source and a secondary power source, a second input coupled to a backup power source, and an output, the sequences of computer-executable instructions including instructions that instruct at least one processor to:
- determine, responsive to receiving a signal indicating that the secondary power source is prepared to provide secondary power to at least one load, an energy level of the backup power source;
- determine, responsive to receiving the signal, whether the energy level of the backup power source is above a threshold energy level;
- and
- control, responsive to determining that the energy level of the backup power source is above the threshold energy level, the UPS system to provide output power derived from the backup power source and not from the secondary power source to the at least one load.