On Battery
APC UPS
Severity: ModerateWhat Does This Error Mean?
The On Battery alarm (continuous beeping every few seconds) means the UPS has lost mains power and is running your equipment from its internal battery. This is normal and expected during a power cut — the UPS is doing its job. Save your work immediately and shut down the computer gracefully if power does not return within 1–2 minutes.
Affected Models
- APC Back-UPS series (BE, BX, BVX)
- APC Back-UPS Pro series (BR, BN)
- APC Smart-UPS series (SUA, SMT)
- APC Easy-UPS series
Common Causes
- Mains power failure — building power cut, blown fuse, or tripped circuit breaker
- Loose or damaged power cable between the UPS and the wall socket
- Faulty wall socket not delivering consistent power
- Brownout — mains voltage dropped too low for the UPS to pass through
- UPS transfer switch fault causing it to switch to battery unnecessarily
How to Fix It
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Save all open documents immediately. The battery provides only a few minutes of runtime — use that time to save work, not to continue working normally.
Battery runtime depends on the load. A computer and monitor typically get 5–15 minutes on a standard Back-UPS. APC PowerChute software can automate safe shutdown when battery reaches a low threshold.
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Check whether the building has lost power or just the socket. Look at other lights and devices. If only the UPS circuit is affected, check the fuse box.
A tripped circuit breaker is the most common cause of a single-circuit power loss. Reset the breaker and the UPS will return to mains power automatically.
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If power has genuinely failed, shut down the computer normally and turn off the UPS to conserve battery. Restart everything once mains power is restored.
Leaving the UPS running on battery with no mains power will eventually deep-discharge the battery, which can shorten its service life.
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If the On Battery alarm fires but mains power is present, check the input power cable and try a different wall socket. If it continues, the UPS transfer switch may be faulty.
Install APC PowerChute software to log when and how often the UPS switches to battery. Frequent brief switches indicate a noisy or low-quality mains supply.
Frequently Asked Questions
How long will an APC UPS run on battery?
Runtime depends on the UPS model and the load. A typical Back-UPS BE650 powering a desktop PC and monitor provides 5–10 minutes. APC's website has a runtime calculator — enter your UPS model and connected devices to get an accurate estimate.