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FACTORS AFFECTING BATTERY PERFORMANCE

Batteries have limited life, usually showing a slow degradation of capacity until they reach 80 percent of their initial rating, followed by a comparatively rapid failure. Regardless of how or where a UPS is deployed, and what size it is, there are four primary factors that affect battery life: ambient temperature, battery chemistry, cycling and service.

1) AMBIENT TEMPERATURE

The rated capacity of a battery is based on an ambient temperature of 25°C (77°F). It’s important to realize that any variation from this operating temperature can alter the battery’s performance and shorten its expected life. To help determine battery life in relation to temperature, remember that for every 8.3°C (15°F) average annual temperature above 25°C (77°F), the life of the battery is reduced by 50 percent.

2) BATTERY CHEMISTRY

UPS batteries are electro-chemical devices whose ability to store and deliver power slowly decreases over time. Even if you follow all the guidelines for proper storage, usage and maintenance, batteries still require replacement after a certain period of time.

3) CYCLING

During a utility power failure, a UPS operates on battery power. Once utility power is restored, or a switch to generator power is complete, the battery is recharged for future use. This is called a discharge cycle. At installation, the battery is at 100 percent of rated capacity. Each discharge and subsequent recharge reduces its relative capacity by a small percentage. The length of the discharge cycle determines the reduction in battery capacity. Lead-acid chemistry, like others used in rechargeable batteries, can only undergo a maximum number of discharge/recharge cycles before the chemistry is depleted. Once the chemistry is depleted, the cells fail and the battery must be replaced.

4) MAINTENANCE

Battery service and maintenance are critical to UPS reliability. A gradual decrease in battery life can be monitored and evaluated through voltage checks, load testing or monitoring. Periodic preventive maintenance extends battery string life by preventing loose connections, removing corrosion and identifying bad batteries before they can affect the rest of the string. Even though sealed batteries are sometimes referred to as maintenance-free, they still require scheduled maintenance and service. Maintenance-free simply refers to the fact that they don’t require fluid. Without regular maintenance, your UPS battery may experience heat-generating resistance at the terminals, improper loading, reduced protection and premature failure. With proper maintenance, the end of battery life can be accurately estimated and replacements scheduled without unexpected downtime or loss of backup power.

What can go wrong with batteries?

Plate separation: Due to repeated cycling (charging and discharging), damage during handling and shipping, and overcharging.
Grid corrosion: Due to normal aging, operating in an acidic environment and high temperatures.
Internal short circuit: Due to heat (plates expand causing shorts), separator failure, handling and shipping, and grid corrosion.
External short circuit: Due to human error (shorting terminals) and leaks.
Sulfation of plates: Due to sitting discharged for an extended period, not on charge or being undercharged.
Excessive gassing: Due to often due to high temperatures or overcharging.
Drying out: Due to excessive gassing, high temperatures or overcharging.

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