How to determine what size backup battery is needed

The UPS And Determining The Required Capacity

Calculate battery power of the UPS (battery voltage) * Ah. (Voltage multiplied by amp hours)

Time = (inverter efficiency * battery voltage * Ah) / load in watts)

How to size a UPS

List the amps and volts for each device. (These ratings can typically be found on the label on the back of the equipment.) Multiply the number of amps by the number of volts to determine VoltAmps (VA). (Some devices may list their power requirements in watts.)

1. List all equipment to be protected by the UPS. 

2. List the amps and volts for each device.

3. Multiply the VoltAmps (VA) by the number of pieces of equipment to get the VA subtotals.

4. Add the VA subtotals together.

5. Multiply the total by 1.2 to get the grand total. 

6. Use the grand total to determine the volt and amps required in the backup battery.