Fix or replace your power supply when short backup runtime shows up?

Fix or replace your power supply when short should start with repeatable checks, not guesswork. Test settings, drivers, thermals, power behaviour, and recent changes so SA readers can isolate the cause before buying parts.

Build Lab · 26 Jun 2026 · 3 min read · PowerWise ·

Fix or replace your power supply when short backup

Quick Answer

When short backup runtime shows up, that is a UPS battery issue, so replace the battery or the unit rather than the PC's power supply. UPS batteries wear out in 3-5 years and lose runtime; if a once-reliable UPS now dies in seconds, fit a fresh battery or buy a new pure sine wave unit (1000VA/600W around R2,500-R4,000) sized to your real draw.

Short runtime points to the UPS battery, not the PC

If your UPS used to hold for minutes and now cuts out in seconds, the battery has aged, not the computer's power supply. Sealed lead-acid UPS batteries degrade over 3-5 years and lose capacity. The fix is a replacement battery of the correct rating, or a new unit if the UPS is old or the battery is not user-replaceable.

Replace the battery or the whole unit

Many UPS units take a standard replacement battery, which restores runtime for a fraction of a new unit's cost. If the UPS is several years old, lacks a serviceable battery, or only ever gave a clean shutdown window, replacing the whole unit with a pure sine wave model around R2,500-R4,000 is the cleaner long-term choice. Match the VA to your actual load.

Right-size so runtime meets your need

Short runtime can also mean the unit was always too small for the load. A 1000VA/600W pure sine wave UPS suits a PC and monitor pulling around 350W, giving a comfortable shutdown window. If you need more minutes, size up. Measure your draw with a plug meter so the new battery or unit actually delivers the runtime you expect.

FAQ

Why has my UPS runtime dropped to seconds?

The battery has aged. Sealed UPS batteries lose capacity over 3-5 years, so a once-reliable unit now dies quickly. Fit a fresh replacement battery or buy a new unit; the PC's power supply is not the cause.

Should I replace the UPS battery or the whole unit?

Replace just the battery if the UPS is otherwise good and takes a standard cell. If it is several years old or the battery is not serviceable, a new pure sine wave unit around R2,500-R4,000 is the better long-term choice.

How do I get more UPS runtime?

Right-size the unit to your draw and consider a larger VA rating. Measure your PC and monitor load with a plug meter, then choose a battery or unit that delivers the runtime you actually need.

Short backup runtime is the UPS battery, not the PC: fit a fresh battery if the unit takes one, or replace it with a pure sine wave 1000VA unit sized to your measured draw.