The Elgar GUPS Series of uninterruptible power supplies are ruggedized on-line UPSs that accept a broad range of worldwide utility and military AC input power. Without operator intervention, they automatically select the appropriate input power ranges to accommodate global operation. The batteries used in the GUPS Series units are a spiral wound, valve-regulated, lead-acid batteries. While the unit itself maximizes battery life with automatic, microprocessor-controlled equalization and temperature compensation during charging, there are steps that users can take to extend UPS battery life even more.
What shortens UPS battery life?
Sulfation, a natural electrochemical reaction in lead acid batteries, is the primary culprit, but other phenomena also shorten UPS battery life. These include:
- nonoperational discharge,
- cell impedance,
- operating and storage temperature,
- the number and depth of discharges and charger characteristics.
Sulfation. In normal operation, a chemical reaction between the sulfuric acid electrolyte and the lead plates in a battery forms lead sulfate crystals. These crystals behave like insulation, hindering the battery’s ability to accept a charge. Sulfation also causes an increase in cell impedance. The rate of sulfation increases when the battery is exposed to higher temperatures, when the battery is stored for a long time without a recharge, and when the battery is stored in a discharged state.
Non-operational discharge. Even when powered down, the GUPS Series units draw a small current (300-500 µA). Users can remove the battery drawer from the GUPS chassis, but the batteries will continue to self-discharge when not in use. If the GUPS is stored without being recharged after the battery is used, the additional self-discharge will damage the battery
Cell impedance. Sulfation causes an increase in cell impedance, and eventually this increase in impedance will reduce the battery's output voltage full charge. Sooner or later, the batteries will be unable to power the GUPS.
Operating and storage temperatures. Higher operating and storage temperatures reduce battery life by increasing sulfation rates.
Number and depth of discharges and charger characteristics. When operating a GUPS at higher temperatures, the charge voltage must be temperature-compensated by reducing the voltage to avoid an over voltage. At lower temperatures the charge voltage must be temperature-compensated by increasing the charge voltage to prevent undercharging. Although these charger related parameters are outside an end user’s control, they are taken into account in the GUPS system design.
How to make batteries last longer
While it is impossible to eliminate sulfation or self-discharge, there are some things that users can do to improve battery life, including:
- recharge a discharged battery before storing it,
- store the battery at a cool temperature, and
- charge a battery for 72 hours prior to using it after it has been in long-term and/or high-temperature storage.
Another thing that users can do is to control operating temperatures, When and where possible, reduce the operating temperature will reduce sulfation, thereby extending battery life.
- Keep the battery charged and cool.
- Remove the battery drawer from the GUPS chassis if you need to store the batteries for more than 30 days.
- Do not store the battery drawer in a discharged state.
- Recharge the battery after use and before storing.
- Store at lower temperatures. A fully charged battery drawer can be stored for 10 months at 10º C, but at 40º C this is reduced to 1.5 months.
- Before use after long-term storage, charge the batteries in the chassis for 72 hours.
Finally, consider placing the GUPS batteries on a cyclic life-extension maintenance schedule where the chassis-in-use is swapped out with a stored battery drawer, at intervals frequent enough to minimize the effects of long-term storage, storage at high temperatures, and self-discharge.