Later, sealed batteries emerged, mainly valve-regulated lead-acid (VRLA) batteries. Since they do not require water addition, VRLA batteries were called maintenance-free batteries from the start, and manufacturers promised a service life of 10 to 20 years (at least 8 years). This led domestic technical and maintenance personnel to misunderstand that these batteries are both durable and completely maintenance-free. Many users basically performed no maintenance or management after installing the batteries. Consequently, in the early 1990s, VRLA batteries used domestically encountered many new problems not previously seen, such as battery case deformation, electrolyte leakage, insufficient capacity, and uneven terminal voltages. These phenomena occurred not only domestically but also abroad, where VRLA batteries were adopted earlier than in our country.
In VRLA batteries, due to higher electrolyte specific gravity and larger float current, electrode corrosion is more rapid. Electrode corrosion also consumes oxygen, causing the battery to dry out, which is a unique failure mode of VRLA batteries. These can all lead to electrolyte leakage. Some VRLA battery failures are caused by malfunctioning gas regulating valves. Cooling is more critical for VRLA batteries than for open-type batteries; if insufficient, thermal runaway may cause the battery to melt or explode. Corrosion and fracture of internal terminals, inter-cell connectors, and electrode joints are also more frequent in VRLA batteries than in open-type batteries. These failures all result in capacity loss. This makes it difficult for users to assess the durability and failure issues of VRLA batteries.
User and management units often focus only on the maintenance and management of the equipment part of the backup power supply, neglecting the significant role of the battery bank, unaware that the danger of power failure largely lurks in the battery bank. The charging characteristics of the entire battery bank are such that if one or several aged batteries with increased internal resistance exist, their capacity will inevitably decrease. When the charger charges the battery bank, the aged batteries, due to their small capacity, will quickly become fully charged. The charger will mistakenly think the entire bank is fully charged and switch to float charging, supplying constant voltage and small current. The other healthy batteries cannot be fully charged. The battery bank will charge and discharge based on the capacity of the aged batteries. Through a vicious cycle of float charge-discharge-equalizing charge-discharge-float charge, the capacity continuously decreases, and the backup time shortens.
Conclusion: If not regularly tested to identify and adjust aged batteries, the capacity of the battery bank will decrease, battery life will shorten, and the efficient and safe operation of the system will be affected.
More rapid electrode corrosion: In VRLA batteries, due to higher electrolyte specific gravity and larger float current.
Battery drying out: Electrode corrosion also consumes oxygen, causing the battery to dry out.
Battery melting or explosion: Cooling is more critical for VRLA batteries than for open-type batteries.
Corrosion and fracture of internal terminals, inter-cell connectors, and electrode joints are also more frequent in VRLA batteries than in open-type batteries.
All of these can lead to capacity loss.
