How Long Can a UPS Keep Equipment Running?
UPS runtime is not a fixed number — it depends on load, battery size and battery health. Here is how to think about it when specifying a system.
"How long will the UPS keep us running?" is the question we are asked on almost every site survey. The honest answer is: as long as you have paid for in battery capacity — and no longer.
Runtime is a function of load
A UPS rated at 10 kVA does not give you 10 minutes of runtime at any load. It gives you a certain battery capacity, and the runtime depends on how much of that capacity the load draws. At 100% load you might get 5–10 minutes; at 50% load, considerably longer. The relationship is not linear because of inverter efficiency and battery discharge characteristics.
What are you actually sizing for?
There are only two sensible design targets:
- Enough runtime to ride through a brief outage and keep running — typically 5–15 minutes.
- Enough runtime to start a standby generator or complete a graceful shutdown — typically 10–30 minutes.
Sizing for hours of battery autonomy is almost never cost-effective; that is what a generator is for. The UPS bridges the gap, it does not replace generation.
Our UPS runtime calculator turns your load and target runtime into a kVA recommendation in seconds — and shows the battery cabinets needed to hit it.
Talk to an engineer about your power protection
We specify, supply and maintain Riello UPS systems across the UK. Tell us about your load and we will recommend the right system.
