Short answer
UPS battery life depends on the manufacturer's design life, the temperature of the room it works in and how many times it has been deeply discharged. Even if a battery looks sound from the outside, its capacity drops over the years, and when the power goes out the UPS cannot last the expected time. Batteries should be tested at least once a year, checked more often in hot rooms, and batteries in the same string should be replaced together.
Why does a UPS battery weaken without being noticed?
Most UPS units use sealed lead-acid batteries. These batteries stay on constant charge inside the UPS or in a cabinet next to it. As long as the power does not go out, nobody needs the battery, and whether anything is wrong with it stays invisible.
The battery's capacity falls over time through chemical aging. A UPS that lasts twenty minutes in the first year may shut down within a few minutes under the same load a few years later. On the UPS front panel everything looks normal, because the battery's voltage is at normal values while on standby. The problem shows up only when the battery actually carries the load.
That is why most battery problems are discovered when the power goes out and the server or recorder shuts down unexpectedly. Unfinished operations on a server that shuts down, a corrupted database or a lost camera recording cost far more than replacing the battery.
How does temperature affect battery life?
Battery manufacturers usually give the design life for a room temperature between 20 and 25 °C. As the temperature rises above this, chemical aging inside the battery speeds up and its life is noticeably shortened. A battery that sits in a constantly hot room may need replacing far sooner than the period stated in the catalog.
In summer in Şanlıurfa, an electrical room without air conditioning, an under-stair space or a storeroom that gets sun are the places where UPS batteries fail most often. The UPS itself also produces heat while running. A UPS and battery string placed inside a cabinet with no ventilation work in an environment hotter than the room temperature.
The most effective way to extend a battery's life is to keep it cool. The room where the UPS and battery cabinet are located should be air-conditioned, and there should be a temperature sensor that alerts you when the air conditioner fails.
Expert note: Place a simple temperature logger next to the UPS and look at the records over a summer. The daytime values may reassure you; the real problem appears on weekends when the air conditioner is switched off or fails.
When should the battery be replaced? Warning signs
The time to replace a battery is determined not only by the calendar but also by the test result. If you see any of the signs below, do not delay a battery test:
- Replace-battery warning on the UPS front panel or in its software
- The UPS shutting down sooner than expected during a short outage
- An automatic battery test ending in failure
- Swelling or cracks in the battery case, or white deposits on the terminals
- Odor or overheating coming from the battery compartment
- Batteries approaching the manufacturer's design life
- 1Monitor room temperature
- 2Keep the automatic test on
- 3Run a discharge test once a year
- 4Find weak batteries by measuring
- 5Replace the string together
- 6Hand in the old battery at an authorized point
How is a battery test done?
Most UPS units have an automatic battery test feature. This test transfers the load to the battery for a short time and looks at the battery's voltage behavior. The test must be set to run at regular intervals. If the UPS has a management card or software, test results and warnings can be reported by e-mail.
A short test catches a battery that is completely depleted, but it does not show exactly how much capacity has dropped. A more reliable method is a discharge test with the real load during a planned maintenance window. This test shows how many minutes the UPS lasts at today's load. If the result is shorter than the time the system needs, a battery replacement is planned.
In large battery strings, the voltage and internal resistance of each battery are measured individually. A single weak battery in the string lowers the performance of the whole string, and it is found with this measurement.
What to watch for when replacing batteries
Batteries in a string are connected in series and work together. Replacing only the faulty one with a new one makes the old batteries and the new battery behave differently in the same string. The new battery soon drops to the level of the old ones. That is why batteries in the same string are replaced together, with batteries of the same model and the same production period.
The capacity, size and connection type of the new battery must match what the UPS requires. Batteries that sit in storage for a long time discharge on their own; a battery with a very old production date should be checked before it is installed.
Many UPS units allow battery replacement while running. Even so, during the replacement the load is left without a battery, and if the power goes out at that moment the system shuts down. For critical systems, battery replacement is done at a planned time. Battery terminals can deliver high current; the replacement should be done by trained technical staff.
What is done with old batteries?
Lead-acid batteries are classified as hazardous waste and are not thrown in the trash. Old batteries are handed in to the waste battery collection system or to authorized collection points. Ask the company doing the battery replacement how the old batteries will be disposed of.
In organizations, battery replacement dates, the model of the replaced batteries and test results should be kept in a maintenance logbook or a digital record. This record shows when the next replacement is needed. Sticking a label on the batteries with the date they were installed is also a simple but useful habit. When the IT person in charge changes or the maintenance company changes, it is possible to tell the battery's age from this label.
How much backup time do you need?
Battery capacity determines how long the UPS will last. If the aim is to ride out short outages and shut servers down properly, a few minutes may be enough. If you want camera recording to continue during long outages as well, a larger battery string or generator support is needed. The UPS calculator on our site shows the approximate time for a camera system; the tool's result is for new batteries.
As the battery ages, the time gets shorter. When choosing a UPS and determining battery capacity, if the lower capacity a few years later is also taken into account, the system will provide the time needed throughout its life.
Frequently asked
How many years until a UPS battery needs replacing?
It depends on the battery's design life, the room temperature and the number of discharges. In hot rooms the life is noticeably shorter. The decision should be based on test results rather than the calendar.
Can I replace only the faulty battery?
Not recommended. Batteries in the same string work in series; a new battery used together with old ones soon drops to the level of the old ones. The string is replaced together.
My UPS gave a battery warning but the power isn't going out. Is it a problem to wait?
The warning shows that the battery may not be able to carry the load during an outage. The system may shut down at the first outage. Battery testing and replacement should not be delayed.
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