A malfunction in the VRLA will cause the entire battery string to fail.
No technology can guarantee that it will not suddenly fail, so regardless of the solution used, battery technology with dual battery strings is required.
Plan a reasonable battery replacement cycle. Under ideal conditions, batteries will fail within the expected timeframe. When a cell in a battery string fails, replace the entire string. New batteries have different electrical characteristics than old ones, and mixing new and old batteries in a string can lead to more failures. There is an exception to this rule: battery failures occurring within six months of the replacement.
Battery monitoring is also necessary. Many UPS systems come with battery monitors, but third-party monitoring may be more accurate. Some UPS battery monitors measure the battery’s internal resistance, while others apply a very small voltage for test runs. One vendor claims that battery monitoring can rebalance battery strings, so you can mix and match new and old batteries. However, manufacturers state that no monitor can accurately predict whether a battery failure will occur.
The electrolyte in VRLA batteries may dry out after a period of time, but battery failure is mainly caused by repeated charge-discharge cycles and unstable mains voltage; overheating in abnormal environments; and overcharging can also lead to overheating. All of these will shorten the UPS battery’s lifespan and may cause battery cracking and leakage. Overcharging may also cause hydrogen emissions.
Battery warranties are structured, so their value drops rapidly in the early years. For example, if a battery is advertised as “10 years” but fails after only 3 years, its warranty value can easily fall to less than half.
An environment below 77 degrees Fahrenheit (25 degrees Celsius) allows batteries to operate most stably. Many UPS systems are often located in the same room as servers, rather than in a separate battery room. Since ASHRAE raised the recommended operating temperature for IT equipment, inlet air can now exceed 77 degrees Fahrenheit, and exhaust hot air can potentially exceed 100 degrees Fahrenheit (38 degrees Celsius). This needs to be considered before introducing a UPS into a server room. Tests show that increasing battery temperature by 15 degrees Fahrenheit (8.3 degrees Celsius) can reduce UPS battery life by 50%.
Batteries generate heat during charging and discharging, so they need to be cooled as soon as possible after a power outage is restored. Without a backup generator to support the cooling system, the continued deep discharge and increased temperature of the battery will significantly reduce its lifespan.
There is no reason to overcharge the UPS battery. A good charger has temperature monitoring and compensates by reducing the charging current when the temperature rises.
Even with proper maintenance, VRLA UPS battery life should not be expected based on theoretical values, especially under less than ideal conditions. Any type of battery monitoring is far better than no monitoring at all.