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Common UPS Failure Points and Preventive Maintenance

Oct 21
5 min read

Updated: Oct 22

A UPS only protects your equipment if it works when the power drops. This guide pulls together what UPS makers Eaton, Schneider Electric (APC), Vertiv and Xtreme Power Conversion publish about why UPS systems fail and how to maintain them.

1. Batteries

Eaton calls batteries "the number one cause of UPS failure" and describes valve-regulated lead-acid (VRLA) batteries as "the leading cause of UPS failure and load loss" (Eaton, 6 tips; Eaton, UPS installation).

What wears them out, according to the makers:

  • Age. Eaton says VRLA batteries need replacement every three to five years on average. Schneider says most APC batteries should last three to five years (FA158934). Xtreme's P91 and P80 manuals give a battery service life of 3 to 5 years at 25 °C ambient (Xtreme P91 manual; Xtreme P80 manual).

  • Heat. Schneider says operating at higher temperatures significantly reduces battery lifespan. It notes that the battery inside a UPS always runs warmer than the room, and strongly recommends a location with good airflow, proper ventilation and adequate cooling (FA158934). Eaton says heat can significantly reduce battery service life (Eaton, 6 tips) and that a UPS should never be placed in direct sunlight (Eaton, UPS installation). For temperature limits, follow your UPS and battery maker's published guidance, such as the operating temperature in your UPS manual.

  • Discharges. Schneider says to run runtime calibrations only once or twice a year, and only if truly necessary, because frequent calibrations shorten battery life. It also says a UPS isn't designed for frequent deep-discharge cycles (FA158934).

  • Storage. A stored battery loses charge on its own. Schneider says an APC battery loses 3% of its capacity per month at 20 °C and 10% per month at 40 °C (FA156516). Recharge stored batteries on your UPS maker's schedule. Schneider's is at least every six months at –15 to +30 °C and at least every three months at +30 to +45 °C. Xtreme's P91 manual says to charge the UPS for 5 hours before storage, then recharge every 3 months at –25 to 40 °C and every 2 months at 40 to 45 °C (Xtreme P91 manual).

Schneider lists the signs of an aging, sulfated VRLA battery: longer charging times, excess heat, shorter runtimes and a much shorter overall life (FA158934). For more on replacement timing, see When to Replace a UPS Battery.

2. Overload

Schneider recommends never loading a UPS above 80%, to leave headroom for inrush current when equipment starts. A badly overloaded UPS may shut down or trip its circuit breaker to protect itself, which powers off everything plugged into it (FA156513). Eaton adds that loads change over time, so check that your UPS isn't running over capacity (Eaton, 6 tips). To check your numbers, see How to Size a UPS.

3. Batteries that never get a full charge

Schneider describes a UPS that goes to battery again and again for short periods because of power problems you may not notice. Those brief trips can drain the battery, because the UPS never spends long enough on line to recharge fully, and the UPS can eventually shut down (FA156513).

4. Heat, dust and blocked airflow

  • Eaton says never to block UPS vents and not to stack items on top of a UPS, because both can cause overheating (Eaton, UPS installation).

  • Eaton warns that caked-on grime can damage fans and cause electronic board damage, and that a simple wipe-down is often enough (Eaton, 6 tips).

  • Follow the clearances in your UPS manual. Xtreme's P91 manual, for example, asks for at least 100 mm at the front and bottom and 300 mm at the back and both sides (Xtreme P91 manual).

5. Loose connections

Eaton notes that connections can shift inside a UPS during shipping. Loose connections can lead to sparking, charring or even fires. Eaton says any hardwired UPS should be installed by a licensed electrician (Eaton, UPS installation).

6. Aging fans and capacitors

Vertiv describes capacitors as UPS parts that age gradually in service, losing capacitance as their resistance rises. It says aging fans can lead to overheating and cause the load to transfer to bypass, which leaves it unprotected (Vertiv, UPS Capacitor & Fan Replacement). Vertiv recommends replacing fans and capacitors on a planned schedule before they fail. The interval depends on the equipment, so use the schedule from your UPS maker.

7. Setup and wiring issues

Schneider lists other reasons a Smart-UPS can drop its load: ground loops (for example, one device with two power supplies, one on the UPS and one on utility power), the wrong serial cable, outlet groups configured off, and emergency power off (EPO) wiring set up incorrectly (FA156513).

Preventive maintenance checklist

  • Yearly check-up. Eaton recommends a preventive maintenance exam at least once a year (Eaton, 6 tips). As an acceptable minimum, Vertiv's guide lists 1–2 visits a year for a UPS under 60 kVA and 2–4 for one over 60 kVA (Vertiv, Maximizing the Reliability of Your Equipment).

  • Battery age. For smaller UPSs, Eaton says to note the battery's age and plan a replacement once it's four years or older.

  • Self-test. Run the UPS battery self-test. For APC units, see How to Run an APC UPS Self-Test.

  • Look for swelling or damage. Eaton suggests removing the front panel of smaller UPSs to check the batteries for swelling or damage. Check your manual first. Xtreme's P91 manual, for example, says only service personnel can replace its internal batteries (Xtreme P91 manual).

  • Keep it clean and cool. Keep airflow clear, dust the unit and inspect electrical connections visually (Eaton).

  • Check alerts. If the UPS has a network card, send a trial email alert and keep the UPS and card firmware up to date (Eaton).

  • Keep records. Keep warranty and service contract details in one place, register the UPS with its maker, and keep the operator's manual where you can find it (Eaton).

  • Recheck the load. Confirm the UPS isn't running over capacity (Eaton) and stays at or below 80% (Schneider).

When the UPS warns you

  • Replace-battery warning. On a Smart-UPS, Schneider says to charge the battery to 100% (at least 8 hours, or 24 hours with external batteries connected), then run a self-test with the normal load attached. If the Replace Battery light stays on, replace the battery (FA156584). Xtreme's P91 manual says that when the battery-replacement icons flash and the alarm sounds every 2 seconds, it's time to replace the batteries, and to contact your service representative (Xtreme P91 manual).

  • Short backup time. Xtreme's P91 manual says to charge the batteries for at least 5 hours and then check capacity, and to consult your dealer if the problem continues. It lists a defective battery as the other possible cause, with replacement as the fix (Xtreme P91 manual).

Need replacement batteries or UPS service?

We supply replacement UPS batteries and battery trays and provide service across the Southeast USA. Replacement trays for Xtreme P91 and P80 lead-acid models: P90-BAT1 · P90-BAT2 · P90-BAT3 · P90-BAT4.

Request current price and availability: use the request form or email office@luxena.net.

Sources (checked 2026-10-21)

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