In modern society, reliable power supply is crucial for homes, offices, and corporate data centers. The Uptime Institute’s 2024 Annual Power Outage Analysis Report indicates that electricity remains the leading cause of power outages (52%). To minimize this, a UPS (Uninterruptible Power Supply) has become essential, and the core component is the UPS battery.

What is a UPS Battery

A UPS (Uninterruptible Power Supply) is a device that provides short-term power when utility power is interrupted. It is commonly used to protect computers, network equipment, medical instruments, and critical hardware in data centers. In addition to supplying power during outages, it can also improve power quality through filtering and voltage regulation. In a UPS system, the battery (UPS Battery) is the core component for energy storage. When utility power is normal, the battery remains in charging or standby mode; once an outage occurs, the battery immediately delivers power through the inverter to the load, ensuring uninterrupted operation. The main functions of a UPS Battery include providing power assurance, preventing hardware damage from power fluctuations, avoiding data loss, and improving power quality to some extent.

Main Types of UPS Batteries

Common types of UPS Batteries include VRLA (Valve-Regulated Lead-Acid), lithium-ion batteries, nickel-cadmium batteries, and some emerging battery technologies.

• VRLA (Valve-Regulated Lead-Acid) batteries are currently the mainstream UPS battery type, divided into “AGM (Absorbent Glass Mat)” and “GEL” types. Due to low cost (less than half the price of lithium batteries), good temperature tolerance (operating from -15°C to 40°C), mature technology, and high safety, they are widely used, especially in small to medium enterprise server rooms and household UPS.
• Lithium-ion batteries have become increasingly popular in recent years. With high energy density, lighter weight (about half that of VRLA), long cycle life (1,000–2,000 charge/discharge cycles before degrading to 80%, which is 2–4 times longer than VRLA), and high charging/discharging efficiency, they are gradually becoming the mainstream choice for high-end data centers and enterprise-grade UPS.
• Nickel-cadmium batteries are considered “traditional batteries.” They perform well in harsh environments (-40°C to 60°C) but have significant drawbacks: memory effect (capacity shrinks if not fully discharged before recharging), environmental issues due to cadmium, and low energy density (larger in size compared with VRLA for the same capacity). They are mainly used in specialized scenarios.
• Lithium polymer batteries and UltraBatteries are emerging. The former is lightweight and flexible, suitable for portable UPS, while the latter combines lead-acid and supercapacitor technologies, offering both stability and long life.

Working Principle of UPS Batteries

A UPS system usually consists of a rectifier, inverter, battery pack, and control system. The rectifier converts AC into DC to charge the battery; the inverter converts the DC released from the battery into AC to power the load; the battery pack handles energy storage and release; the control system monitors the battery state and switches power modes when needed. When utility power fails, the battery immediately takes over and outputs stable AC through the inverter. This process typically takes 2–10 milliseconds and almost never affects equipment operation.

UPS Battery Selection and Capacity Calculation

When selecting a UPS Battery, the first step is to calculate the required capacity based on load power. For example, if a system includes a 500W server and a 100W switch, the total power is 600W. You should then select a UPS rated at 1.2–1.5 times the load, i.e., 720VA–900VA. Next, determine the number and capacity of battery packs based on desired backup time. Different application scenarios require different capacities:

• Home offices typically use 600VA–1000VA UPS with 10–15 minutes of backup.
• Small enterprises are advised to choose 2–5kVA UPS with 30+ minutes backup.
• Data centers usually require 10–500kVA UPS with backup times of several hours, often combined with generators.

Extending runtime requires adding more batteries, but cost, space, and cooling must be considered. UPS type also influences battery choice: offline UPS typically use small VRLA batteries, line-interactive UPS are suited for office use, while double-conversion online UPS—commonly used in data centers—are paired with large lithium battery packs.

UPS Battery Installation and Maintenance

Proper installation of UPS Batteries is vital to system stability. During installation, check battery type and polarity to avoid reverse connections or compression, and ensure clean, oxidation-free contacts. The optimal operating temperature is 20–25°C; high temperatures drastically shorten lifespan. Humidity should be controlled to avoid leakage and corrosion, and good ventilation is necessary to prevent overheating. UPS Batteries require regular maintenance, including quarterly discharge tests to verify performance, and monitoring of voltage, internal resistance, and temperature via a Battery Management System (BMS). Common issues include swelling (caused by overcharging or high temperatures), capacity degradation (due to age), and abnormal charge/discharge (possibly inverter or charging circuit faults).

UPS Battery Lifecycle and Replacement

UPS Battery lifespan depends on environment, charge/discharge cycles, depth of discharge, and load size. Lead-acid batteries typically last 2–5 years, lithium-ion batteries 5–10 years, and nickel-cadmium batteries 8–15 years. Replacement is needed when capacity drops more than 30%, swelling or leakage occurs, or normal charge/discharge is no longer possible. Old batteries contain heavy metals like lead and nickel and must be recycled through certified channels to avoid environmental pollution.

Advantages and Limitations of UPS Batteries

The primary advantage of UPS batteries is that they provide security for critical loads, preventing data and equipment damage. As technology advances and costs decrease, their adoption is increasing. However, different battery types have their own advantages and disadvantages: lead-acid batteries are inexpensive but have a short lifespan; lithium batteries have a long lifespan but are expensive; and nickel-cadmium batteries are durable but pose pollution risks.

The IEA special report, “Batteries and Secure Energy Transitions,” shows that the use of lithium-ion batteries in the global energy sector is growing rapidly, while lithium-ion battery prices are steadily declining. Lithium-ion batteries and new energy storage technologies are gradually replacing traditional lead-acid batteries and are being combined with renewable energy sources (such as solar and wind power) to promote the development of green UPS systems.