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 did not perform any maintenance or management after installing the batteries. Consequently, in the early 1990s, many new problems that had not been encountered before appeared in VRLA batteries used domestically, such as battery case deformation, electrolyte leakage, insufficient capacity, and uneven terminal voltage. These phenomena occurred not only domestically but also in foreign countries that adopted VRLA batteries earlier than China.
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. This is a unique failure mode of VRLA batteries, and these issues can lead to electrolyte leakage. Some VRLA battery failures are caused by malfunctions in the gas regulating valve. Cooling of VRLA batteries is more important than for open-type batteries; if insufficient, thermal runaway may cause the battery to melt or explode. Internal terminals, inter-cell connectors, and electrode joint corrosion and breakage are also more frequent in VRLA batteries than in open-type batteries. These failures all result in capacity loss, making it difficult for users to grasp the durability and failure issues of VRLA batteries.
User units and management units often only emphasize the maintenance and management of the equipment part of the backup power supply, while neglecting the significant role of the battery pack. They are unaware that the danger of power failure largely lurks in the battery pack. The charging characteristics of the entire battery pack 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 pack, the aged batteries, due to their small capacity, will quickly reach full charge. The charger will mistakenly assume that the entire pack is fully charged and switch to float charging, providing constant voltage and small current to the pack. The other healthy batteries cannot be fully charged. The battery pack will charge and discharge based on the capacity of the aged batteries. After multiple cycles of float charge - discharge - equalizing charge - discharge - float charge, the capacity continuously decreases, and the backup time of the battery pack shortens.
Conclusion: If not regularly tested to identify and adjust aged batteries, the capacity of the battery pack 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 of VRLA batteries is more important than for open-type batteries.
Internal terminals, inter-cell connectors, and electrode joint corrosion and breakage are also more frequent in VRLA batteries than in open-type batteries.
All of these can lead to capacity loss.
