This article outlines the steps to evaluate a battery bank’s health, which starts with a visual inspection of the battery bank’s location, its enclosure, and the condition of the batteries themselves. Next, specific measurements are made, including testing battery voltages and checking the electrolyte in each cell for its level, specific gravity, temperature, and color.
The information collected during a battery assessment can be used to track the changes in a battery over time; analyze the impact of charging setpoint adjustments; or review the performance of a battery with the manufacturer or supplier. This data is particularly useful when replacement is necessary, and when you need to determine what changes should be made in the system’s settings and operation to achieve better performance and longer battery life.
The first step of a visual inspection involves making general observations about the battery bank and its enclosure or room. This includes checking if the batteries are protected from the weather; if there is good airflow to keep the batteries cool and to dissipate hydrogen gases; and verifying that necessary safety equipment is accessible. Each battery must be checked for problems such as bulging cases, cracks, leaks, and corrosion. Next, the system’s setpoints need to be reviewed and recorded. Finally, the condition of the charging system’s battery temperature sensor is evaluated.
Battery bank location is important, as it can affect the amount of ventilation available to dissipate heat and hydrogen/fumes produced by the battery. The location should also provide protection from weather extremes—such as shading from the sun or insulation from cold. The bank also needs to be isolated from any sources of flame or spark (such as a gas-fired water heater), which could ignite hydrogen produced by the batteries.
Workspace clearances and safety. There needs to be easy and safe access for maintenance. Live parts of the battery (terminal posts and cable connections) should be guarded against accidental contact. Clearance and equipment accessibility are important to safe system maintenance and are required by the NEC (see “Code Corner” in HP156). The battery room should not be used as a storage space—impeded access to the battery bank can discourage maintenance and can also affect airflow.
Adequate safety gear should be available for maintenance and repair. This includes goggles, chemical-rated gloves, insulated tools, and a nonmetallic flashlight. A supply of baking soda and distilled water should be kept with the batteries. A Class C-rated fire extinguisher should also be located at the entrance of the room in case of an emergency.
The condition of the battery enclosure and rack needs to be evaluated, since corrosion from a metal enclosure or rack to a battery terminal can result in ground faults or shock hazard. The enclosure or rack should include spill containment trays or liners to handle spills from overfilling or leaks. There should be air vents in a battery enclosure (bottom and top) to allow air to enter and exit. All metal enclosures or racking should also be connected to the grounding system.
Assess the battery’s overall condition. Bulging battery cases may be caused by swollen plates, which have been damaged from overcharging. Dirt- or debris-covered battery tops can increase the battery’s self-discharge and result in contamination of the electrolyte. Melted battery terminals may be evidence of arcing from loose connections, or from a direct short-circuit during maintenance. Corrosion on the terminals can reduce performance and lead to imbalanced charging between paralleled strings of batteries. The battery makes and models must all be the same and the same age; mixing different battery manufacturers or models will result in uneven charging and reduce the batteries’ performance and life.