When to Replace UPS Batteries
Most UPS batteries should be replaced every 3 to 5 years, or sooner if the UPS fails a self-test, shows a replace-battery alarm, or delivers noticeably less runtime than expected. Batteries are the most common cause of UPS failure, so replacing them on schedule is the single most effective way to keep a UPS ready for an outage.
This guide covers battery lifespan, warning signs, testing, hot-swap replacement, and disposal.
How long do UPS batteries last?
Most UPS systems use sealed valve-regulated lead-acid (VRLA) batteries, also called sealed lead-acid (SLA) or AGM batteries.
- Typical service life: about 3 to 5 years at 25 °C (77 °F) for standard VRLA batteries in small and mid-size UPS systems.
- Design life vs service life: a battery's published "design life" (for example 5 or 10 years) is measured under ideal lab conditions. Real service life is usually shorter.
- End of life: the industry convention is that a battery has reached end of life when its capacity falls to 80 percent of its rated value. Below that point, capacity tends to decline quickly.
Lithium-ion UPS batteries are available in some newer models. They generally last longer than VRLA batteries, often 8 to 10 years or more, but they cost more and must be replaced with the manufacturer's approved battery for that UPS.
What shortens UPS battery life?
Temperature
Heat is the biggest factor. A widely used rule of thumb is that VRLA battery life is cut roughly in half for every 8 to 10 °C (about 15 to 18 °F) above 25 °C (77 °F). A battery expected to last 4 years at 25 °C (77 °F) may last about 2 years in a 33 °C (91 °F) closet.
Keep UPS batteries in a cool, ventilated space. Network closets without dedicated cooling are a common cause of early battery failure.
Discharge cycles
Each outage that runs the UPS on battery uses part of the battery's life. Frequent outages, deep discharges, and repeated generator-transfer tests all shorten service life.
Charging conditions
Batteries kept at the wrong float voltage, or connected to a UPS with a faulty charger, can age faster. Firmware and charger checks are part of preventive maintenance.
Storage time
Batteries age even when not in use. A battery that sat on a shelf for a year before installation has already used part of its life. Check the date code on replacement batteries before installing them.
What are the warning signs of a failing UPS battery?
Replace or test UPS batteries when you see any of these signs:
- Replace-battery alarm or LED on the UPS display
- Failed self-test reported by the UPS or monitoring software
- Short runtime: the UPS shows less estimated runtime than it did when new, or shuts down sooner than expected during an outage
- The UPS drops the load during a brief outage or transfer
- Swollen, cracked, or bulging battery cases
- Leaking, corrosion, or residue around terminals
- A sulfur or "rotten egg" smell, which can indicate a battery overheating or venting
- Batteries that are hot to the touch
- Batteries at or past 3 to 5 years of service, even with no alarm
A swollen or hot battery is a safety issue. Do not keep using the UPS. Contact a qualified technician.
How do you test UPS batteries?
Built-in self-test
Most UPS systems run a self-test automatically on a schedule, typically every 7 to 14 days, and can run one on demand. A self-test briefly places the UPS on battery and checks that voltage holds. It catches batteries that have failed outright, but it does not measure full capacity.
Runtime calibration test
A runtime calibration test discharges the batteries under the real load to measure actual runtime. It gives the UPS a more accurate runtime estimate. Run it during a maintenance window, because the batteries are left partly discharged and need time to recharge.
Voltage and impedance testing
During a maintenance visit, a technician can measure each battery or battery string. Voltage readings find batteries that will not hold charge. Internal resistance or impedance readings find batteries that are aging before they fail. Trending these readings over time is the best early warning.
Load-bank testing
On larger systems, a load bank can test the UPS and batteries at a known load without risking production equipment.
The right test depends on the UPS, its batteries, and how critical the load is. GreenlightUPS includes battery testing in every preventive maintenance visit and tailors additional battery testing to your needs.
Should I replace all UPS batteries at once?
Yes. In most UPS systems, batteries are wired in series strings. A string is only as strong as its weakest battery, and a new battery placed next to aged batteries will be overworked and age quickly.
Replace every battery in a string, or every battery in the UPS, at the same time. Use batteries of the same type, capacity, and age. For modular systems such as APC Symmetra, replace battery modules in matched sets per the manufacturer's guidance.
Can UPS batteries be hot-swapped?
Many UPS systems support hot-swap battery replacement, which means batteries can be changed while the UPS is online and still powering the load. This is common on:
- Rack-mount and rack/tower UPS units with front-access battery cartridges, such as the APC Smart-UPS SRT series
- Modular UPS systems with removable battery modules, such as APC Symmetra LX and PX
During a hot-swap, the load stays powered by utility power, but it is not protected by battery while the batteries are disconnected. Schedule the swap at a low-risk time and keep the disconnected interval short.
Some tower and larger three-phase systems are not hot-swappable. They require the UPS to be placed in maintenance bypass or shut down. Always follow the manufacturer's procedure for your model. For a step-by-step example, see our Symmetra PX battery replacement guide.
How do I choose the right replacement battery?
Match the replacement to the UPS:
- Model and part number. Use the manufacturer's replacement battery number, such as an APC RBC cartridge or SYBT module, or an equivalent with identical specifications.
- Voltage and amp-hour capacity must match the original.
- Terminal type and connectors must match.
- Physical size must fit the battery bay.
- Chemistry. Do not substitute lithium-ion for VRLA, or the reverse, unless the manufacturer supports it.
- Date code. Choose fresh batteries.
GreenlightUPS lists replacement batteries and battery modules in UPS Add-Ons. Listings include APC Symmetra battery modules such as the SYBT5 and SYBTU1, APC replacement battery cartridges, and Vertiv APS battery modules. Batteries and battery trays bought on their own, without our installation, have no formal warranty, because we can't control the environment they are installed in, but we will work with you on any problem that comes up within a reasonable time after delivery. Batteries inside a UPS you buy from us are covered by that unit's warranty.
How should old UPS batteries be disposed of?
Do not put UPS batteries in regular trash. Lead-acid batteries contain lead and sulfuric acid and are regulated as hazardous materials in the United States. They are also among the most recycled products: the lead and plastic are recovered and reused.
Options for disposal:
- Return to the battery supplier if they offer take-back. When GreenlightUPS replaces your batteries, on-site or by ship-in, we take the old ones back and recycle them free of charge.
- Use a licensed battery recycler or a local hazardous-waste program.
- Ask your service provider to remove and recycle batteries as part of the replacement visit.
Before shipping used batteries, tape the terminals and package them upright. Shipping lead-acid and lithium batteries is subject to transport regulations, so check with your carrier.
What is a good UPS battery replacement schedule?
Record the installation date on every battery set. A simple label on the UPS saves guesswork years later.
Does GreenlightUPS replace UPS batteries?
Yes. GreenlightUPS sells replacement UPS batteries and provides UPS battery replacement service as part of its critical-power field service. Our own technicians replace batteries on-site nationwide, and ship-in replacement is also available. When GreenlightUPS supplies the batteries and installs them on-site, the batteries and the installation carry a 1-year warranty. Call 954-366-3070 or use our contact form with your UPS model and serial number.
Frequently asked questions
How often should UPS batteries be replaced?
Most VRLA UPS batteries should be replaced every 3 to 5 years at 25 °C (77 °F), and sooner in hot rooms or after frequent outages.
How do I know if my UPS battery is bad?
Common signs are a replace-battery alarm, a failed self-test, short runtime, swelling, leaking, a sulfur smell, or batteries that are hot to the touch.
Can I replace UPS batteries without turning off the UPS?
Yes, if the UPS supports hot-swap batteries. Many rack-mount and modular UPS systems do; some tower and three-phase systems require bypass or shutdown.
Should I replace all the batteries in a UPS at once?
Yes. Replace every battery in a string at the same time with matching type, capacity, and age.
How do I dispose of old UPS batteries?
Recycle them through a battery supplier take-back program, a licensed battery recycler, or your service provider. Do not put them in regular trash.
Need replacement batteries?
Shop replacement batteries and battery modules, or book on-site battery replacement nationwide. Call 954-366-3070 with your UPS model and serial number.
GreenlightUPS was founded in 1981 and serves customers nationwide.