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ITGlossary · UPS technology
Autonomy
The time a battery-powered system (like a UPS) can continue operating critical loads after a power failure.
Technical level:Basic
Runtime depends mainly on two factors: the load you are powering and the battery capacity. A small line-interactive UPS with internal batteries usually provides only a few minutes at full load, roughly 3–10, while at half load the time is often more than double, because batteries perform better under gentler discharge. Longer times are achieved with external battery banks.
Before choosing a UPS, decide what you really need: a few minutes for a safe computer shutdown, time until a generator starts, or hours of operation without mains. Manufacturers' runtime tables give the time for each load level.
Remember that runtime decreases as batteries age or when the room is hot. Run a periodic runtime test so you do not discover the problem during the next outage.
Related terms
- MTTR (Mean Time To Repair)The average time it takes to repair a system after a failure occurs.
- Zero Transfer TimeA feature of online UPS systems, where the inverter feeds the load continuously so a power cut causes no gap at all.
- Auto RestartA UPS feature that automatically restarts the system after utility power returns following a shutdown.
- MTBFThe average operating time between failures of a device, used as a measure of its reliability.
- Transfer TimeThe brief power gap when a UPS switches from mains to battery, typically 2–10 ms for line-interactive models and zero for online ones.
- AC EfficiencyIndicates how efficiently a UPS converts incoming AC power into usable output power during normal operation.