Can You Replace VRLA UPS Batteries with Lithium? What to Check First

If your UPS is currently using VRLA batteries and the batteries are approaching end of life, you may be considering a lithium UPS battery replacement. But can you simply remove the VRLA batteries and install lithium batteries instead?

Sometimes, but not as a simple drop-in replacement.

A VRLA-to-lithium upgrade depends on the UPS's DC bus voltage, charging characteristics, battery power requirements, communication interface, physical installation space, and protection requirements. Matching the nominal voltage and capacity alone does not guarantee compatibility.

For data centers, industrial facilities, and other critical-power applications, the right approach is to evaluate the existing UPS and battery system as an integrated system before selecting a lithium replacement.

What Should You Check Before Replacing VRLA with Lithium?

Before choosing a lithium UPS battery, start with the specifications of the existing UPS and VRLA battery system.

1. UPS DC bus voltage and battery operating range

Check the UPS's required battery voltage and the acceptable battery operating-voltage range.

A lithium battery may have a similar nominal voltage to the existing VRLA configuration but a different voltage curve and operating range. The lithium battery system must remain within the UPS's acceptable input range during both charging and discharge.

2. Charging voltage, current, and charging profile

VRLA and lithium batteries do not necessarily use the same charging parameters.

The replacement battery therefore needs to be evaluated against the UPS's charging voltage, current limits, charging logic, and protection settings. In some retrofit projects, UPS firmware, control parameters, or other system settings may also need to be reviewed.

3. Required backup power and runtime

The lithium system must provide sufficient discharge power for the UPS load as well as the required backup runtime.

This is particularly important for high-power UPS applications. A battery can have sufficient energy capacity in kWh but still be unsuitable if its discharge power or voltage characteristics do not meet the UPS requirements.

For detailed battery capacity calculations, see ACE Battery's guide to how to calculate UPS battery size.

4. Physical installation and connections

Check the available cabinet or rack space, battery dimensions, weight, connectors, cable configuration, ventilation or cooling requirements, and installation method.

Lithium systems can offer a significant space advantage over conventional VRLA battery banks, but the replacement still needs to fit the existing installation and meet the project's mechanical requirements.

The key point: electrical compatibility, mechanical compatibility, and system integration all need to be evaluated together.

Does the Lithium Battery Need to Communicate with the UPS?

In many lithium UPS applications, battery management is more sophisticated than simply monitoring battery voltage.

A lithium battery system normally incorporates a Battery Management System (BMS) to monitor and protect the battery. Depending on the system design, the BMS may monitor:

• State of charge (SOC)

• State of health (SOH)

• Cell and battery temperature

• Charging and discharging current

• Overvoltage and undervoltage conditions

• Overcurrent and other protection conditions

The UPS and battery system may also need to exchange operating and alarm information through interfaces such as CAN, RS485, Modbus, or dry contacts.

This means a lithium battery can meet the required voltage and capacity specifications but still require additional communication or BMS integration before it can operate correctly with an existing UPS.

For an upgrade project, confirm:

• Which communication protocol the UPS supports

• Whether the lithium BMS supports the required protocol

• What alarms and battery status information need to be exchanged

• Whether firmware or control settings need to be modified

• How the system should respond to battery protection events

For large UPS systems, this communication layer is an important part of the compatibility assessment rather than an optional feature.

Should You Use a Standard or Custom Lithium UPS Battery?

Once the electrical and system requirements are understood, the next question is whether a standard lithium UPS battery is suitable or whether a customized solution is required.

When can you use a standard lithium UPS battery?

A standard solution may be appropriate when:

• The UPS is designed to support lithium batteries

• Battery voltage and operating range are compatible

• Charging parameters are supported

• Required power and runtime fall within the battery's specifications

• BMS communication is supported

• The battery cabinet or rack fits the installation

• Standard connectors, protection functions, and configurations meet the project requirements

In these cases, a standard lithium UPS battery system can simplify deployment and shorten the integration process.

When is a custom lithium UPS battery required?

Customization becomes more relevant when the existing UPS or project has non-standard requirements, such as:

• A specific DC voltage or battery configuration

• Proprietary UPS communication protocols

• Custom BMS functions or communication mapping

• Limited rack or cabinet space

• Specific connector, cable, or mechanical requirements

• High discharge-current requirements

• A discontinued or difficult-to-source VRLA battery configuration

• Integration into an OEM UPS or industrial system

• A project requiring repeated battery production rather than a one-off replacement

For these projects, the objective is not simply to find a lithium battery with the same Ah rating. The battery system may need to be engineered around the UPS's electrical, mechanical, communication, and operating requirements.

What Are the Benefits of Upgrading from VRLA to Lithium?

When the existing UPS is suitable for a lithium retrofit, the upgrade can provide advantages beyond replacing an aging battery.

Higher power density and lower space requirements

Lithium battery systems can deliver higher power from a more compact battery configuration than conventional VRLA banks.

For example, ACE Battery's U300, U400, and U500 lithium battery cabinets are designed as DC backup power systems for medium- and large-power UPS applications. According to ACE's system specifications, the cabinets are designed to support over 1/2 MW of discharge power in a 19-inch IT cabinet, with approximately 70% less space occupancy than VRLA batteries.

This can be particularly valuable in data centers and enterprise computer rooms where rack and floor space are constrained.

Longer design life and lower replacement frequency

The U300/U400/U500 systems have a 15-year design life, compared with approximately three times the design life of conventional VRLA batteries under ACE's stated specifications.

A longer service life can reduce the frequency of battery replacement projects, as well as associated labor, downtime planning, and maintenance requirements.

High-power performance for large UPS systems

High-power UPS applications can require batteries capable of delivering substantial current during short-duration backup events.

ACE's U300/U400/U500 systems use high-C-rate lithium battery modules and support configurable cabinet architectures for approximately 200–500 kW UPS backup power requirements. A single cabinet can accommodate 8–12 battery modules, with 600A, 800A, or 1000A frame-current options. Multiple cabinets can also be connected in parallel for larger requirements.

The configuration can therefore be matched to different UPS power and runtime requirements rather than relying on a single fixed battery configuration.

Integrated BMS and system protection

A lithium UPS battery system also provides more active battery monitoring and protection through its BMS.

The U300/U400/U500 systems use a three-level BMS protection structure and incorporate intelligent charging and discharging control based on operating conditions such as power, temperature, and battery SOH.

The systems use LFP battery technology and include thermal-runaway protection and verification measures. The systems are specified to comply with UL9540A, UL1973, and UL1642.

More flexible communication and monitoring

For projects requiring remote battery monitoring or integration with existing power-management systems, communication capability can also be important.

The U300/U400/U500 systems support interfaces including CAN, RS485, RS232, USB, dry contact, and Modbus TCP/IP, along with an LCD interface and remote monitoring/OTA capabilities.

The appropriate interface depends on the UPS and project architecture, so communication compatibility should still be confirmed during system evaluation.

What Information Should You Provide for a VRLA-to-Lithium Upgrade?

If you are evaluating a lithium replacement for an existing VRLA UPS battery system, providing the following information can help a battery supplier determine whether a standard solution is suitable or whether customization is required.

UPS information

• UPS manufacturer and model

• Rated UPS power

• DC bus voltage

• Battery charging specifications

• UPS battery communication interface

• Available UPS manuals or technical documentation

Existing battery information

• VRLA battery manufacturer and model

• Battery voltage and Ah capacity

• Number of batteries

• Series/parallel configuration

• Existing battery cabinet or rack dimensions

Project requirements

• Required backup runtime

• UPS load or required discharge power

• Available installation space

• Operating temperature and installation environment

• Communication requirements

• Required certifications

• Initial project quantity and expected production volume

With this information, the battery supplier can assess the electrical and mechanical requirements before recommending a replacement architecture.

Considering a VRLA-to-Lithium UPS Upgrade?

Replacing VRLA batteries with lithium is not simply a matter of matching voltage and capacity. The UPS, battery, BMS, communication system, and physical installation all need to work together.

For standard applications, an off-the-shelf lithium UPS battery may be sufficient. For high-power UPS systems, data centers, industrial equipment, or OEM projects with specific voltage, communication, mechanical, or power requirements, a custom lithium UPS battery system may provide a better fit.

ACE Battery provides customized lithium battery solutions for UPS and critical-power applications.

Share your UPS model, existing VRLA battery specifications, required backup runtime, and project requirements with ACE Battery. Our team can evaluate the electrical compatibility, BMS and communication requirements, mechanical integration, and system configuration to determine the appropriate lithium UPS battery solution.