Published by Battery Plex
Emergency light fixtures are a staple in all large industrial, commercial and multi-unit residential complexes. During a power outage, they are designed to come on automatically, supplying at least 90 minutes of illumination that allows the building's occupants to safely exit, and, in the case of a fire, earthquake, or other natural disaster, they are designed to provide emergency responders with enough light to make sure that the building has been cleared of occupants. After the power is restored, the emergency light batteries are then automatically recharged, so they are ready for the next time power is lost.
Code requirements in many municipalities stipulate that emergency light batteries must provide a full 90 minutes of illumination, but there are several factors that could reduce their performance, and may require that the batteries be replaced with a new set.
Here are a few of the things that can affect the performance of emergency light batteries:
#1 Age of the Batteries
Age is the most important factor in how well emergency light batteries perform. Under standard conditions, sealed lead acid, or SLA, emergency light batteries can be expected to last about 5 to 7 years. Emergency light batteries based on nickel metal hydride technology, or NiMH batteries, can last between 2 and 5 years. Both types of batteries can withstand hundreds of charge and discharge cycles, but when they are used in a standby situation, the stored power will slowly be reduced due to the self-discharge effect present in all types of batteries, and they will eventually need to be recharged. This means that even though they are not actively being discharged, they will still experience a charge and discharge cycle.
As the batteries approach the end of their lifespan, their overall storage capacity will be reduced, and eventually, the emergency light batteries will no longer produce the required 90 minutes of illumination. At this point, they will need to be replaced in order to satisfy code requirements in most municipalities.
#2 Operating Temperature
The ambient temperature in the building can greatly affect the performance of some emergency light batteries, especially those based on SLA technology. In commercial and residential buildings that are kept at even temperatures, this is not much of a problem. But in some industrial and commercial applications where extremely low or high temperature are expected, such as refrigeration facilitates or foundries, the temperature extremes can greatly effect battery performance.
In low temperatures, SLA batteries can suffer from reduced capacity, leading to emergency lights that provide a shorter period of illumination than batteries kept at room temperature. When the temperatures are near or below freezing, the battery capacity can be significantly reduced, by over 50 percent, and if the batteries are kept in a discharged state below freezing, they may even be permanently damaged. To compensate for operation at low temperatures, a battery with a higher capacity may be required.
At high temperatures, the overall service life of an SLA battery will be reduced, due to inefficient charging at high temperatures and chemical changes that happen within the battery itself. By increasing the normal operating temperature from 77 to 92 degrees, a battery that is expected to last 10 years may only last 5 to 7 years. To extend the life of SLA batteries, keep them as close to room temperature as possible.
NiMH batteries are less susceptible to temperature changes, and all but the most extreme temperatures will not affect operation, lifespan or capacity significantly.
#3 Lack of Maintenance
Proper maintenance is required to keep emergency light fixtures and their batteries operating properly. Though SLA or NiMH batteries do not require regular maintenance like flooded lead acid batteries, which must have their electrolyte levels and condition checked regularly, they still must be kept at a proper state of charge and they must go through the charge and discharge cycle periodically to maintain the proper capacity.
It is a good idea to check all emergency light fixtures monthly to make sure they are working properly by disconnecting the power and ensuring that they illuminate. Every three or six months, they should be put through a full charge and discharge cycle, by disconnecting the power and allowing the lights to operate until they shut off. The period of illumination should be timed, to make sure that it is at least 90 minutes, and they should be allowed to recharge fully after the test. If any of the lights fail to illuminate for the full 90 minutes, their batteries should be replaced.
Overcharging a battery can generate excessive amounts of heat, and cause damage to the battery, significantly shortening its lifespan. Emergency light fixtures have a built-in recharging circuit that automatically recharges the battery to the correct capacity, but if the charging circuit is damaged or the wrong type of battery is installed, the battery may be overcharged and damaged. Make sure to replace defective emergency light fixtures, and only replace the battery with the same type, whether it is NiCD, NiMH or SLA-based.
#5 Storing Batteries in a Discharged State
If emergency light batteries are to be stored and not used for an extended period of time, such as spare batteries for the building's fixtures, they must be fully charged before storing them. Batteries stored in a discharged state for even a short period of time may be damaged permanently. Make sure to fully charge batteries before storing them, and recharge them at least every six months. Replace any emergency light fixtures that have a defective charging circuit, so that the fixture's batteries are always kept properly charged and protected from accidental discharge.
By knowing how these factors affect the performance of your emergency light fixtures, you can make sure that your emergency light fixtures are always ready in the event of power loss or a natural disaster. When your emergency light batterers no longer produce the required 90 minutes of illumination, consult the owner's manual for each fixture and replace the battery with one of the same type and capacity.