Stationary batteries: will yours work when you need them?

Stationary batteries are designed for use at a fixed location. They have a long life expectancy and can be recharged several times. In most applications, the actual use of batteries (discharge) is relatively infrequent and only occurs during power outages. This means a battery typically operates in float mode (to maintain its charge) for most of its service life. Currently, three main battery types dominate the market, even though new technologies such as lithium-ion batteries are emerging and being closely watched. These three categories are:

• Vented lead-acid (VLA)
• Valve-regulated lead-acid (VRLA)
• Nickel-cadmium (Ni-Cd)

VLA batteries are popular with public utilities because they have a proven track record in the field. VRLA and Ni-Cd batteries are often preferred for industrial complexes because these stationary stored-energy power sources have low maintenance requirements and fewer electrical room engineering constraints. However, these systems are not entirely maintenance-free.

When is corrective action required?

A number of factors can cause battery inefficiency, including:

• Unsuitable ambient temperatures
• High levels of airborne contaminants (dust, dirt, etc.) in industrial environments
• Inadequate float voltage
• Excessive recharging leading to electrolyte loss

Periodic inspections and performance tests can help you determine the right operating conditions for your batteries and make adjustments as needed to maximize their service life. When inspecting batteries or before performing capacity tests, make sure to:

1. Measure the specific gravity of the electrolyte (if applicable).
2. Check and adjust electrolyte levels.
3. Remove any corrosion, excess dirt or potassium carbonate (greyish white deposits) from cells or connectors.
4. Verify all bolted connections.
5. Measure voltage and internal ohmic resistance across each cell.
6. Check the float voltage at the battery terminals. Verify battery charger settings and adjust as needed.

Any other abnormal conditions should be corrected and documented.

Performance testing

Periodic performance testing is the only way to make sure your batteries will work properly when you need them.

An initial performance test of the battery capacity should be made:

1. VLA batteries: Within the first two years of service.
2. VRLA batteries: Upon installation.
3. Ni-Cd batteries: Within the first two years of service and having the battery on float charge for at least 12 weeks.
4. Thereafter, additional performance tests should be carried out at the following intervals:
5. VLA batteries: Intervals between performance tests should not exceed 25% of the expected service life.
6. VRLA batteries: Intervals between performance tests should not exceed 25% of the expected service life or two years, whichever is shorter.
7. Ni-Cd batteries: Performance tests should be carried out every five years until the battery shows signs of excessive capacity loss.

Battery condition also affects how frequently tests should be performed. Annual performance testing is recommended for all types of batteries that show signs of excessive capacity loss or degradation since the previous test, and for batteries that have reached 85% of their expected service life.

Battery monitoring systems

Today, a wide range of continuous monitoring devices are available for all types of battery systems. They could play an important role within a predictive maintenance program and could help maximize battery life, reduce maintenance and replacement costs, and enhance the safety of your critical battery backup systems. Of course, they can also prevent costly downtime.

When was the last time you conducted performance testing on your stationary battery systems? How would your facilities be affected if your backup systems failed during a power outage?

Developing and implementing an effective maintenance program for your stationary battery systems can help you prevent unexpected incidents.