A UPS is only useful if it is sized for the real load and the real runtime you need.
## Measure the actual load Add up the wattage of every device on the protected circuit, then add 25% headroom for growth.
## Decide the runtime Do you need five minutes to shut down gracefully, or two hours to keep working? Runtime drives battery bank size and cost far more than the UPS rating does.
## Choose the topology Line-interactive suits offices. Online double-conversion is the right choice for server rooms and telecom equipment where power quality matters.
## Don't forget battery maintenance Batteries are consumables. Plan replacement every three to five years and test them under load annually.