During normal operations, emergency exit signage and lighting receive power from a building’s electrical grid. However, when that power is interrupted, the signage and lighting’s power reserve is activated, and the fixture provides light via a backup power source. An internal rechargeable battery within the lighting fixture often provides this power.
Because these emergency exit signs and lights are a building occupant’s lifeline to safety in an emergency, they must be reliable. Building codes and life safety laws mandate key requirements for backup power to ensure reliability. An emergency exit sign and light must be rechargeable, with a charge time of fewer than 24 hours, and provide enough electrical current to keep the lamps lit for a minimum of 90 minutes when the unit is engaged.
There are four main types of batteries used in emergency exit signage and lighting: Lead Calcium batteries, Ni-Cad (Nickel-Cadmium) batteries, Lithium Iron Phosphate batteries, and Nickel-Metal Hydride batteries.
Lead Acid and Lead Calcium Batteries – Great Choice for Inverters and Hazardous Location Lights & Exit Signs
Lead-acid batteries are the oldest form of rechargeable batteries. The original lead-acid battery contained antimony, calcium, tin, and selenium lead electrodes, which were high maintenance and heavy. They are rarely used today but can still be found in some central battery backup systems.
The new generation of lead batteries is Lead Calcium Batteries. This type of lead-acid battery has only calcium and lead as the electrode inside the battery. It is fully sealed, eliminating the need to check the water levels and making it a maintenance-free battery. Lead Calcium batteries are more efficient than their predecessor. They are resistant to corrosion, perform better in cold weather, have a low self-discharge rate (meaning they will work for an extended period), and have no excessive gassing.
Lead Calcium batteries are ideally suited where lower upfront costs are a consideration. They also store a higher capacity in amp-hours, and the temperature doesn’t significantly affect capacity and self-discharge. Lead calcium batteries are best in terms of reliability and working capability. They tolerate slow, fast, and overcharging better than other batteries and can withstand long-term inactivity.
Most emergency signage and lighting, including steel emergency lights, wet location emergency lights, and hazardous location emergency lights, use lead-acid type batteries. Also, if a remote headlamp is needed, lead-calcium batteries can be configured to accommodate the extra voltage required to support the lamp. Because of their reliability, lead-calcium batteries are also used in most inverter units. https://isolite.com/inverters/
Nickel–Cadmium Batteries (Ni-Cd or NiCad) – The choice for exit signs and lighting that requires small batteries
The nickel-cadmium battery (Ni-Cd battery or NiCad battery) is well suited for emergency lighting and signage applications where their small size and light weight are necessary considerations. These cylindrically shaped AA-sized batteries offer numerous advantages over traditional sealed lead-acid battery types using nickel oxide hydroxide and metallic cadmium as electrodes.
NiCad batteries are often used in indoor applications where thermoplastic emergency lights are recommended. They perform well in rigorous working conditions, such as extreme temperatures, and can be installed in any orientation without considering battery acid. This compact battery also boasts a fast recharge time of as little as 3.5 hours and has an extended lifespan of nearly 15 years. While the initial cost is greater than the lead-acid battery, NiCad batteries are lighter weight and cheaper to ship.
The nickel-cadmium battery is not ideal for wet applications or hazardous or explosive-proof fixtures and does not have enough charge to operate remote lamps when needed.
Lithium Iron Phosphate Batteries – Long life span and minimal maintenance
The lithium iron phosphate battery is a type of lithium-ion battery using lithium iron phosphate as the cathode material and graphitic carbon electrode with metallic backing as the anode. Lithium iron phosphate batteries (LiFePO4 or LFP) have a lower energy density and operating voltage than some battery types but are well suited for backup power and are rapidly becoming more widely used.
LiFePO4 batteries offer many benefits compared to lead-acid batteries and other lithium batteries. They are smaller and lighter and available in various dimensions, capacities, and shapes. Lithium iron phosphate batteries have a life cycle of more than 10xs that of lead-acid batteries and perform well under extreme temperatures. Due to their slow discharge rate, LiFePO4 batteries can be stored for more extended periods without active maintenance. They are environmentally friendly, have low toxicity, and won’t overheat or catch fire.
While the initial start-up costs for LiFePO4 batteries may be more than other options in the marketplace, the long-life span and zero maintenance make these batteries cost-effective.
Nickel-Metal Hydride Batteries – High Capacity and Environmentally Friendly
A nickel-metal hydride battery (NiMH or Ni–MH) has a chemical reaction at the positive electrode similar to that of the nickel-cadmium battery. However, the negative electrodes use a hydrogen-absorbing alloy instead of cadmium. NiMH batteries are typically used as a substitute for similarly shaped alkaline batteries, as they feature compatible cell voltage.
NiMH batteries are ideally suited for high-current-drain applications. They can have two to three times the capacity of NiCd of the same size, with significantly higher energy density. Nickel metal hydride batteries have a slightly shorter life cycle than lithium batteries but are more cost-effective.
Nickel Metal Hydride is an environmentally friendly battery. They don’t contain harmful lead, mercury, or nickel that can contaminate drinking water if the batter is not disposed of properly. They are also easy to store and transport because they are not subject to regulatory control.
Make sure your emergency exit signs and lighting contains the right battery for the job.
Isolite emergency lighting experts ensure that our emergency lighting solutions contain the battery backup sources ideal for each fixture and product. Whether it is our Elite Edge-Lit Master Exit sign (https://isolite.com/products/eltmr/ ) with its long-life, high-temperature fused nickel-cadmium battery, our HLX-C (https://isolite.com/products/hlx-c/ ) corrosion-resistant, wet location rated sign powered by a sealed lead-calcium battery, the fully recessed MIGN2 (https://isolite.com/products/mign2/ ) compact LED emergency light powered by maintenance-free nickel-metal hydride battery, or our long-life thermally safe high-capacity lithium iron phosphate battery-powered LED Emergency Drivers, (https://isolite.com/specsheets/EMP-ISOLITE-Specification.pdf), Isolite has the emergency lighting to fit your needs.