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UPS Batteries Explained

Choosing and installing a replacement UPS battery

Some UPS batteries contain sulfuric acid, which makes them volatile and potentially hazardous. Read the manufacturer's instructions and safety guidelines carefully before using, replacing, or disposing of a UPS battery.

Buying a replacement battery cartridge (RBC) for a UPS system can be a straightforward process if you consider the following factors:

  • Compatibility
    Make sure you buy a battery that is compatible with your specific UPS model. Verify the battery dimensions and battery quantity match the original battery you are replacing.
  • Voltage & Capacity
    Look for a battery with a capacity that is equal to or slightly higher than the original battery. This will ensure that your UPS can provide the same level of backup power as before. Verify the battery voltage and capacity (e.g. 12V, 7.2 AH). You can usually find this information on the manufacturer's website or in the UPS manual.
  • Brand
    Stick with reputable brands when buying replacement batteries. This can help ensure that you get a high-quality battery that will last a long time.
  • Price
    Replacement batteries can vary in price, so shop around and compare prices. Don't be tempted to buy the cheapest battery you can find, as it may not be of good quality.
  • Warranty
    Look for a battery that comes with a warranty. This can provide peace of mind in case the battery fails prematurely.
  • Construction
    The battery case should be constructed of either ABS plastic, styrene, or polypropylene, be non-conductive, and have a high resistance to shock, vibration, chemicals, and heat.

If you are not sure which battery you need, contact the UPS manufacturer for guidance.

ups battery replacement

Types of UPS Battery

Valve Regulated Lead Acid (VRLA) Batteries

A VRLA (Valve Regulated Lead Acid) battery is a type of rechargeable battery commonly used in uninterruptible power supplies (UPS) and renewable energy storage.

VRLA batteries are called "valve regulated" because they use a pressure relief valve to control the internal pressure of the battery, which helps to prevent gas leakage and dry-out. The valve also allows the release of excessive gas and prevents the battery from exploding.

VRLA batteries are also sometimes referred to as "sealed lead-acid" (SLA) batteries because they are designed to be maintenance-free, meaning they do not require the addition of water to the cells like traditional flooded lead-acid batteries. This is achieved using a special electrolyte immobilization technology that prevents the electrolyte from spilling or leaking out of the battery.

There are two main types of VRLA batteries - absorbent glass mat (AGM) and gel batteries. AGM batteries use a special glass fiber mat to absorb the electrolyte and keep it in place, while gel batteries use a gelled electrolyte that is immobilized in a silica-based compound. Both types of VRLA batteries offer high energy density, fast recharge times, and long service life, making them an ideal choice for UPS battery backups.

vrla replacement battery for ups

Lithium Ion (Li-ion) Batteries

A Lithium Ion (Li-ion) battery is a type of rechargeable battery used to power a variety of electronic devices, including smartphones, laptops, electric vehicles, and newer UPS systems.

Li-ion batteries use a chemical reaction to store and release electrical energy. They are made up of one or more cells, each containing a positive electrode (cathode), a negative electrode (anode), and an electrolyte solution. The cathode and anode are typically made from materials like lithium cobalt oxide, lithium manganese oxide, or lithium iron phosphate.

During discharge, the lithium ions move from the anode to the cathode through the electrolyte, producing an electrical current that can power a device. During charging, the process is reversed, with the lithium ions moving from the cathode back to the anode.

One of the main advantages of Li-ion batteries is their high energy density, which means they can store a lot of energy in a relatively small size and weight. Li-Ion batteries are typically 40% lighter and half the size of an equivalent VRLA battery. They also have 2-3X longer cycle life, meaning they can be charged and discharged many times before needing to be replaced.

lithium-ion ups battery

72V Lithium-ion Extended Battery Module (EBM) for Eaton 9 Series UPS systems

Lithium-Ion vs Lead Acid Battery Comparison

Feature VRLA (Lead Acid) Battery Lithium-Ion Battery
Charge Cycles 1,000 2,500
Charge Time 8 hours 2 - 4 hours
Average Battery Life 3 - 5 years 8 - 10 years
Footprint 2U - 4U 1U - 2U
Weight 43 - 86 lbs 35 - 53 lbs
Typical Warranty 1 -2 years 5 years
Initial Cost $$ $$$
Replacement Cost $$ $

Further Reading: Eaton Large UPS Battery Handbook

How Long Does a UPS Battery Last?

The lifespan of a UPS battery depends on several factors, including:

  • Type of battery
  • Frequency and depth of discharge
  • Ambient temperature
  • Overall maintenance of the battery

Most sealed lead-acid (SLA) batteries used in UPS systems have an expected lifespan of three to five years. However, this is dependent on the number and depth of discharge cycles the battery experiences, the temperature in which it operates, and the amount of maintenance performed on the battery.

For example, if a UPS battery is frequently subjected to deep discharge cycles, meaning it is drained of a significant amount of its capacity, its lifespan may be reduced. Similarly, if the battery is stored in a hot environment or is not properly maintained, its lifespan may also be reduced.

Lithium-ion batteries used in UPS systems typically have a longer lifespan, with an expected life of five to ten years or more. However, like SLA batteries, the lifespan of a lithium-ion battery can also be affected by factors such as the number of discharge cycles, operating temperature, and maintenance.

4 Tips for Extending the Life of your UPS Battery

Use a high-quality battery
Use a battery that is specifically designed for UPS use and of high quality. Good quality batteries from reputable manufacturers tend to last longer and require less maintenance.

Avoid overcharging
Overcharging can lead to the battery's early deterioration. Make sure to use a UPS with a built-in charging system that can automatically adjust the charging current to prevent overcharging.

Store the battery correctly
Store the battery in a cool, dry place, away from direct sunlight and heat sources. Avoid exposing the battery to extreme temperatures as it can lead to damage. Check and recharge stored batteries regularly.

Proper usage
Use the UPS according to the manufacturer's instructions. Avoid overloading the UPS and use it within its specified load capacity. Never mix old and new batteries. This can reduce the capacity of the new batteries. The combination old and new can also overwork a battery charger.

How to Test a UPS Battery

Regularly testing a UPS battery is important to ensure that it can provide the necessary backup power in the event of a power outage. Here are some steps to test a UPS battery.

  • Schedule a test
    Most UPS systems have a built-in battery test function that allows you to test the battery without disconnecting it from the UPS. Schedule a battery test at least once a year or more frequently if you are in an environment with frequent power outages.
  • Monitor the test
    During the battery test, monitor the UPS to ensure that it is operating correctly, and that the battery is providing the expected amount of backup power. The test will usually take between 15 minutes to an hour, depending on the size and type of the UPS.
  • Check the results
    Once the battery test is complete, review the results to ensure that the battery is operating correctly. Most UPS systems will provide a pass or fail result, and some may provide additional information about the battery's overall health.
  • Perform additional tests
    If the battery test result shows that the battery is not functioning correctly, you may need to perform additional tests to determine the cause of the problem. For example, you may need to test the battery's voltage, capacity, or internal resistance using a multimeter.
  • Replace the battery
    If the battery test result shows that the battery is no longer able to provide sufficient backup power, it may be time to replace the battery. Follow the manufacturer's instructions to safely remove the old battery and install a new one.
ups battery self test

By regularly testing your UPS battery, you can help ensure that it is able to provide the necessary backup power in the event of a power outage.

How to Store a UPS Battery

Storing a UPS battery properly will ensure it remains in good condition and ready to use when needed. Here are some guidelines to keep your UPS batteries in peak condition.

  • Charge the battery - Ensure that the battery is fully charged before storing it. This will help prevent sulfation, a condition that can occur when batteries are left in a partially charged state for long periods of time, leading to permanent damage.
  • Store in a cool and dry place - Store the battery in a cool and dry place, away from direct sunlight and sources of heat or moisture. The ideal temperature range for storing most UPS batteries is between 15 and 25 degrees Celsius.
  • Keep the battery upright - Store the battery in an upright position to prevent leakage or damage to the battery casing.
  • Recharge periodically - If the battery will be stored for an extended period of time, it's a good idea to recharge it every six months to prevent self-discharge and to keep the battery's charge level maintained.
  • Check the battery - Check the battery periodically for signs of leakage or damage. If the battery is damaged or leaking, it should be disposed of properly and replaced.

Further Reading: Top 10 things to know about UPS battery storage life

When to Replace a UPS Battery

It is important to replace a UPS battery when it is no longer able to provide the necessary backup power in the event of a power outage. Here are some signs that it may be time to replace your UPS battery:

  • The battery is more than three to five years old - Most sealed lead-acid (SLA) batteries used in UPS systems have an expected lifespan of three to five years. If your battery is older than this, it may be time to consider replacing it.
  • The UPS indicates a battery problem - Many UPS systems have a built-in battery health indicator that will alert you if there is a problem with the battery. If your UPS indicates a battery problem, it is important to investigate and determine if the battery needs to be replaced.
  • The battery has been subjected to deep discharge cycles - If the battery has been subjected to deep discharge cycles, meaning it has been drained of a significant amount of its capacity, its lifespan may be reduced. In this case, it may be time to replace the battery.
  • The battery is swollen or leaking - If the battery is swollen or leaking, it is likely that it has been damaged and should be replaced immediately. Always use gloves when handling leaking batteries and use baking soda to neutralize any spilled battery acid.
  • The battery is not holding a charge - If the battery is not holding a charge or is not able to provide the necessary backup power, it may be time to replace it.
  • If you are experiencing any of these issues, it is important to investigate and determine if the battery needs to be replaced. By replacing the battery when necessary, you can ensure that your UPS is able to provide the necessary backup power in the event of a power outage.

How to Replace a UPS Battery


A battery can present a risk of high current in the event of a short circuit. High discharge can lead to severe burns and/or the risk of fire. Observe the following precautions when working around high-capacity storage batteries:

  • Remove watches, rings or other metal objects that might come in contact with battery terminals
  • Use tools with insulated handles
  • Wear safety glasses and gloves
  • Do not lay tools or metal parts on top of the battery or near the terminals

Always read and follow the UPS manufacturer's safety instructions.

Replacing a lower capacity (less than 72VDC) prepackaged battery is a relatively simple process, but it is important to follow the manufacturer's instructions to ensure that the replacement is done safely and correctly.

Battery replacement on 3-phase UPS and higher capacity single-phase UPS (5kVA or above) should only be done by a certified technician. Consult your UPS manufacturer for guidance.

Some manufacturers permit "hot swap" battery replacement while the UPS system is powered. Consult your UPS system's owner's manual for guidance.

 replace UPS battery

Here are some general steps to replace a UPS battery.

  1. Power off the UPS
    Before replacing the battery, power off the UPS and unplug it from the wall outlet. If you have a "hot-swap" UPS, you do not need to power down the UPS.
  2. Access the battery compartment
    Open the battery compartment on the UPS. Depending on the model, this may require removing screws or clips.
  3. Document the Battery Wiring
    If possible, take a photograph of the existing battery connections before disconnecting any cables.
  4. Disconnect the old battery
    Carefully disconnect the old battery from the UPS by unplugging the battery cables from the battery terminals.
  5. Remove the old battery
    Carefully remove the old battery from the battery compartment. Be sure to handle the battery safely to prevent damage or leakage. If the old battery has leaked, contact the UPS manufacturer for guidance.
  6. Install the new battery
    Carefully insert the new battery into the battery compartment, ensuring that it is properly seated.
  7. Connect the new battery
    Connect the battery cables to the new battery terminals, ensuring that the connections are tight.
  8. Close the battery compartment
    Close the battery compartment and secure it in place using screws or clips.
  9. Power on the UPS
    After the battery is replaced, power on the UPS and allow it to charge the new battery.

By following these general steps and the original UPS system manufacturer’s instructions, you can replace your UPS battery safely and correctly.

How to Dispose of a UPS Battery

Properly disposing of a UPS battery is important to ensure that it is not harmful to the environment. Here are some guidelines for how to dispose of a UPS battery.

  • Contact a recycling center - Many communities have local recycling centers that accept batteries for recycling. Contact your local recycling center to see if they accept UPS batteries.
    Find a battery recycling center near you
  • Check with the manufacturer - The manufacturer of the UPS battery may have a take-back program for used batteries. Check with the manufacturer to see if they have a program in place.
  • Handle the battery safely - If you are handling the battery yourself, be sure to wear gloves and safety glasses to protect yourself from acid or chemical exposure.
  • Transport the battery safely - When transporting the battery, be sure to secure it so that it does not tip or spill during transport. Use a sturdy, leak-proof container to transport the battery.
  • Do not dispose of the battery in the trash - It is important not to dispose of the UPS battery in the regular trash. This can lead to environmental damage and contamination.

By following these guidelines, you can ensure that your UPS battery is disposed of safely and responsibly.

Never dispose of batteries in a fire; they may explode. Do not open or mutilate the battery. Chemicals released are harmful to the skin or eyes and may be toxic. Follow first-aid procedures for chemical burns in the event of exposure. Use appropriate protective clothing when handling a leaking battery.

How to Add UPS Batteries for Extended Runtime

Adding UPS batteries for extended runtime is a common method used to increase the amount of time that a UPS can provide backup power. Consult your UPS manufacturer for guidance on battery type, model and quantity before attempting to extend UPS runtime.

Lithium-ion extended battery module (EBM)

Questions and Answers

What is battery daisy-chaining?
UPS battery daisy-chaining refers to the process of connecting multiple UPS batteries in series to create a larger battery bank. This is typically done by connecting the positive (+) terminal of one battery to the negative (-) terminal of the next battery and so on, until all the batteries are connected.

When UPS batteries are daisy-chained, the total voltage of the battery bank increases with each additional battery that is added. This can be useful in situations where a long runtime is required.

However, it is important to note that daisy-chaining UPS batteries can also increase the risk of battery failure or damage. If the batteries are not of the same type or age, they may not charge or discharge evenly, which can lead to premature battery failure. Additionally, if the batteries are not properly maintained, they can overheat and cause a fire or other safety hazards.

If you are considering daisy-chaining UPS batteries, seek advice from the UPS manufacturer or a qualified electrician to ensure that it is done safely and effectively.

Can a UPS work without a battery?
To provide a reliable source of power to connected devices, even if the main power supply fails or experiences fluctuations or surges, the UPS needs a battery. The UPS works by converting the incoming AC power to DC power, which is then used to charge the battery. The battery stores the energy, and when there is an interruption in the main power supply, the UPS immediately switches to using the stored energy to provide power to the connected devices.

Without a battery, the UPS can power connected devices but would not be able to provide backup power and would essentially function as a surge protector or line conditioner. While the UPS can help protect connected equipment from power spikes and surges, it does not provide the same level of protection or reliability as a UPS with a battery backup.

It is important to ensure that the UPS battery is properly maintained and replaced as needed to ensure that the system is ready to provide backup power when needed.

Can you replace a UPS battery while the UPS is plugged in?
IMPORTANT: Read the manufacturer's instructions before removing the old battery and installing a new one.

To replace a UPS battery safely, it is recommended to turn off and unplug the UPS. Once the new battery is installed, the UPS can be plugged in and turned on to begin recharging the battery.

If you have a UPS with a "hot swap" feature, you can replace components, such as the battery or power modules, while the system is still in operation.

If the UPS isn’t equipped with a “hot-swap” feature, it will need to be shut down and disconnected from the electrical circuit to avoid any power interruptions or damage to the equipment. This would result in downtime and disruption to the devices connected to the UPS. With a hot swap UPS, however, it is possible to replace components without interrupting the power supply to connected devices. This is accomplished by using a modular design that allows for individual components to be easily removed and replaced while the system is still in operation.

Hot swap UPS systems are often used in critical applications where downtime is not an option, such as in data centers or hospitals. They can help ensure continuous power supply to connected devices and reduce the risk of data loss or system damage in the event of a power interruption or failure.

What is a LiFePO4 battery?
A LiFePO4 battery is a type of rechargeable lithium-ion battery that uses lithium iron phosphate (LiFePO4) as the cathode material. LiFePO4 batteries have several advantages over other types of lithium-ion batteries, including improved safety, longer cycle life, and more stable performance.

The cathode material in a LiFePO4 battery is composed of iron phosphate, which is a more stable and safer material than the cobalt-based cathodes used in other types of lithium-ion batteries. LiFePO4 batteries are less prone to overheating, thermal runaway, and other safety issues that can occur with other lithium-ion batteries.

LiFePO4 batteries also have a longer cycle life than other lithium-ion batteries, with a typical lifespan of several thousand cycles. This means that LiFePO4 batteries can be recharged and discharged more times than other batteries before they begin to lose their capacity or performance.

In addition, LiFePO4 batteries are more tolerant of high temperatures and can operate at a wider range of temperatures than other lithium-ion batteries. This makes them suitable for use in applications such as mines, cell phone towers and traffic light control, where high temperatures or extreme environmental conditions are a concern.

Why Buy from Eaton?

We know you have many brands to choose from. On the surface, they may all seem alike. It's what you don't see that makes the difference. With Eaton, you get solid engineering, proven reliability and exceptional customer service. All our products undergo rigorous quality control before they are offered for sale, and independent testing agencies verify our products meet or exceed the latest safety and performance standards. Our commitment to quality allows us to back our products with industry-leading warranties and responsive customer service. It's the Eaton difference.

Need help with your purchase?
We're always available to help with questions, including product selection, sizing, installation and product customization. Call us at +1 773-869-1776 or email