【2026 UPS Power Supply】One of the batteries in the UPS battery pack has an excessively low voltage; should just that battery be replaced or all of them?
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During the use of a UPS, after it has been in operation for some time, it is common to find that one of the batteries in the UPS’s battery pack swells up. The voltage of this battery is usually low (or its internal resistance is particularly high), while the other batteries show normal readings and appear to be in good condition. In such cases, should one replace just the battery or the entire unit? It is not recommended to replace only one cell; it is advised to replace the entire set.
The main reasons to consider are as follows: 1. There is a significant difference in internal resistance when old and new batteries are used together； This will result in a significant difference in the voltage distribution between the old and new batteries.
2、Using old and new batteries together can also result in voltage differences, leading to an imbalance in charging and discharging.
3. Capacity degradation leads to a \"weak link effect\" – the actual capacity of a battery pack depends on the worst-performing cell within it.
Note: In practice, there are often many factors to consider, such as costs, company policies, lifespan, and business reasons, among others.
For reference below — the six core features of UPS power supplies. I. Reliability: The core of a device’s durability and reliability lies in minimizing malfunctions and ensuring stable operation. The MTBF, or mean time between failures, is commonly used as a benchmark in this industry; high-quality online UPS units can achieve over 100,000 hours of operation. It requires the equipment to maintain stable operation under conditions such as grid fluctuations and frequent startups and shutdowns, preventing issues like unplanned shutdowns and false alarms. By relying on a redundant architecture and high-quality components, it reduces the likelihood of failures – this is the most fundamental hardware requirement for UPS systems.
II. Repairability: The ability to repair faults quickly. Repairability emphasizes fast and simple repairs. Engineers value easy disassembly and modular design, as well as hot-swappable components that allow for replacement without shutting down the entire system. The average repair time for top models in this industry is no more than 30 minutes; their structure is well-organized, the wiring is clearly labeled, and universal spare parts are easily available, all of which significantly reduce the difficulty of repairs and the duration of downtime.
III. Reliability: Comprehensive support throughout the entire lifecycle to ensure peace of mind and thorough coverage. Reliability is focused on providing hassle-free service and complete support at every stage. It covers comprehensive services throughout the entire process, including factory warranty, spare parts supply, technical support, and regular inspections. In simple terms, it means that there are people to repair faults, spare parts are in stock, and inspection plans are in place; a well-developed logistics support system helps reduce potential issues during operation, making it suitable for applications that require continuous operation over long periods of time.
IV. Testability: The ability to quickly diagnose issues. Testability means that it is easier to identify faults and analyze data. Modern UPS units come equipped with an intelligent monitoring system that allows for real-time monitoring of parameters such as voltage, battery capacity, and temperature, and they support self-diagnosis and alarm functions. It enables precise identification of fault locations without the need for complex external instruments, allowing for early detection of potential equipment issues and making it suitable for routine inspections, annual audits, and other testing tasks.
V. Safety: The ability to mitigate risks. Safety is a fundamental requirement, focusing on preventing potential hazards and ensuring the safety of equipment and personnel. A proper UPS is equipped with standard protection against overload, short circuits, lightning strikes, and surges, as well as insulation protection and designs to prevent thermal runaway of the batteries. At the same time, its casing is flame-retardant and complies with grounding standards, preventing safety incidents such as electric leakage, fires, and breakdowns; it is suitable for various demanding usage environments including server rooms and industrial workshops.
VI. Environmental adaptability: The ability to function in complex operating conditions. Environmental adaptability means it can operate in any environment and be used anywhere. Conventional UPS units can operate within a temperature range of 5–40°C, while industrial models are capable of functioning in a wider temperature range and possess properties such as dust resistance, moisture resistance, and vibration resistance. The circuit board is coated with three-proof paint, enabling it to function in environments filled with dust, humidity, and at high altitudes; it can withstand harsh conditions and maintain stable performance.