All emergency lights and exit signs use backup battery packs to provide a minimum of 90 minutes of power when the primary source of electricity is cut. These batteries come in two flavors: nickel cadmium (Ni-Cd) or sealed lead acid. It is important to match the battery type, voltage, and amperage of the new battery with the old one.
Nickel-cadmium batteries are a type of rechargeable battery that use nickel oxide hydroxide and metallic cadmium. This is the same type of battery that is commonly used in portable electronics and toys. They have a variety of uses, but are primarily used in exit signs because they are so small and efficient.
They range in voltage from 1.2V to 6.0V, with larger voltages requiring more cells. Each cell is about the same size as a AA battery. They fully charge in 24 hours and typically maintain their recharge capacity for 5 to 7 years. It is recommended that you reuse your existing nickel-cadmium connectors because wire leads can vary from one manufacturer to another.
Sealed lead acid batteries are another type of rechargeable battery that are used in emergency fixtures. They are similar to nickel-cadmium, but use a slightly different chemical reaction to produce energy. The alloy plates inside the battery are broken down by acid to create charged electrons. This makes for a more powerful battery that powers emergency lights as well as combo fixtures.
These batteries are larger than Ni-Cd, but can support more powerful components. Higher capacity sealed lead acid batteries can extend emergency run times or support more powerful lamps depending on the configuration you have chosen.
THE importANCE OF RELIABLE BATTERIES
There is no doubt that emergency lights and exit signs have the potential to save lives. They can't do it on their own though. They need the help of a reliable battery. When the AC power is cut, it is the sole responsibility of the battery pack to provide enough power to allow the building's occupants enough time to evacuate the premises in an orderly and timely fashion.