How long will a UPS actually run your equipment? It depends far more on the load than on the VA number on the box — the same unit that lasts an hour on a router may give minutes on a desktop. Pick your model, enter the load, and this gives you a planning figure.
Not sure which battery your UPS has? The Battery Finder will tell you from the model number.
What this figure is, and is not
This is a calculation, not a measurement. It takes the battery’s published voltage and capacity, allows 80% depth of discharge because a UPS shuts down before flattening its battery, allows 85% inverter efficiency, and then reduces the result as the load rises — a battery gives up less usable energy the harder you pull on it. That last effect is why doubling the load more than halves the runtime.
What it cannot know is the age and health of your battery, the temperature it lives at, or how your equipment behaves in practice. A three-year-old battery in a warm room can deliver half what a new one does. Use this to plan, then ask us if the number actually matters — for a server or a till, it usually does.
Only models whose battery capacity we publish appear in the list. Where a model ships as a multi-cell pack without a published Ah figure, we have left it out rather than guess — enter the values from the battery label instead, or ask us.
Other tools
Frequently asked questions
How long will my UPS last in a power cut?
It depends almost entirely on the load. The same unit that runs a Wi-Fi router and modem for a long stretch may give only a few minutes on a desktop PC, because the router draws around 25 W and the desktop several hundred. Enter your battery and your load in the calculator on this page for a planning figure.
Why is my real backup time shorter than the calculation?
Three usual reasons: the battery has aged, the room is warm, or the load is higher than assumed. A battery three or more years old can deliver roughly half of what it did when new, which is the point at which it should be replaced.
How do I make a UPS last longer during an outage?
Reduce the load. Take the monitor, printer or anything non-essential off the battery outlets and leave only what must stay running. On a CCTV system, moving the viewing monitor off the battery can nearly double useful recording time.
When should I replace the UPS battery?
A genuine APC RBC cartridge typically lasts three to five years. If backup time has dropped noticeably or the UPS beeps on a brief cut, the battery is the usual cause. The Battery Finder will tell you the exact cartridge for your model.