Sealed Lead Acid vs Nickel Cadmium Emergency Light Batteries
Sealed Lead-Acid Batteries and Emergency Lights
All emergency lights require internal batteries to make them function. These batteries are essential to supply power to the lamps, in the case of a power outage. As such, they must be rechargeable, with a charge time of less than 24 hours and provide enough electrical current to keep the lamps lit for a minimum of 90 minutes when the unit is activated.
There are two types of rechargeable batteries used in emergency lights:
- Lead-Acid batteries
- Nickel-Cadmium batteries
Each of these two have certain advantages and are utilized in specific emergency light applications. Essentially, nickel cadmium batteries are used in thermoplastic emergency lights, where small size is an important consideration.
View our selection of Emergency Light Batteries
Most emergency lights, including steel emergency lights, wet location emergency lights and hazardous location emergency lights use lead-acid batteries. The primary reason for this are:
- Lower acquisition cost
- Higher capacity in amp-hours stored
- Capacity and self-discharge are not highly affected by temperature
Lead-acid emergency light batteries are available in 6, 12 and 24 volts and a wide number of wattage capacities to meet every need. For applications where a remote lamp head is attached to the unit, please indication this need when purchasing so that higher capacity batteries can be installed in the unit.
Lead-acid Battery Maintenance
Lead-acid batteries in emergency lighting are essentially maintenance free. Unlike earlier lead-acid batteries, the ones used today are sealed. This means that there is no requirement to check the water level in the battery and add to it as needed.
The monthly testing of the emergency light unit, using the test button, also tests that the battery is functioning. However, as part of the annual checking of the emergency light unit, disconnecting the battery and checking its voltage is required.
When checking any battery’s voltage, the measured voltage should be slightly higher than the nominal voltage. For example, a new 12 volt battery that is fully charged will normally read 13.2 volts. As the battery ages, the chemical components used to create the electrical charge lose their potential, this is indicated by a reduction in this fully charged voltage. A battery that checks at its stated voltage is very near the end of its life expectancy.
While you can check your batteries with a multi-meter, you are better off using an actual battery tester. The difference between the two is that the batter tester will put a load on the battery and measure the voltage under load. A multi-meter will only check the existing voltage, without any load. In some cases, a battery may check “good” with a multi-meter, but “bad” when put under load.
Nickel-Cadmium Batteries and Emergency Lights
Emergency lights connect to a building's electrical grid when there is available power during normal operations. Should the power cut-off for any reason, the unit's DC battery reserve kicks in and the unit will provide light via rechargeable battery cells.
Battery technology has not changed that much in the past 30 years, and our two battery types have proven reliability time and again:
- Nickel-Cadmium (NiCad) Batteries
- Sealed Lead-Acid Batteries (smaller versions of car batteries)
NiCad batteries are typically utilized in our thermoplastic Emergency Lights, which are designed to be more stylish than classic steel models found in aging police stations and public schools. Because NiCad batteries are smaller than Sealed Lead-Acid, they are the obvious choice for these low-profile Emergency Lights.
Advantages of Nickel-Cadmium Batteries
- Lighter weight
- Smaller size
- Battery can be installed in any orientation, without risk of acid spillage
- Faster charging time
NiCad batteries are efficient, lightweight and each cell is tested to ensure its Emergency Light will illuminate for at least 90 minutes. But unlike the older Sealed Lead-Acid battery powered units, NiCad does not carry enough charge to accommodate a remote lamp.
Maintaining Emergency Lights with NiCad Batteries
Nickel Cadmium batteries will fully charge in 3-1/2 hours and have a "memory" that remembers the peak charge level and will stop charging once it reaches that point. Do not field test the battery backup on your emergency light until it reaches this full charge, or the battery will actually count whatever point it charged to as it's maximum. Conversely, once the battery has been used in a power outage, let it completely drain of power before you re-patch the unit to house power.
As with any Emergency Light, NiCad powered fixtures should be tested once a month and once a year. All Emergency Lights have a test feature which interrupts electrical power to the unit so that it runs solely on the NiCad battery backup unit. If the lamps turn on, the system works fine and you don't have to worry about it for another month.
At the end of the year you'll want to cut building power to the unit for a full 90 minutes or until the unit completely drains of energy. This process does two things; it insures the light will last for 90 minutes as mandated by federal law as well as extend the life of the battery by re-setting it's full-charge memory, as mentioned before.
Replacing NiCad Batteries in Emergency Lights
Nickel Cadmium batteries are easy to spot as they are usually hard-wired to the Emergency Light unit, whereas Sealed Lead-Acid are replaceable and more-or-less resemble AA batteries you might find in a child's toy.
A multi-meter is a good device to test your batteries, though not the most accurate. If your battery is fully charged, the meter will read the voltage as slightly-higher than the battery is rated. Instead use a battery tester instead as they will actually use the battery's juice to do the reading, and batteries on the verge of failing can give faulty readings if tested by a multi-meter.
When replacing NiCad batteries, make sure the cell has the same voltage as the previous. If the replacement battery has too-low a voltage, the unit will not maintain a 90 minute charge. Get one that's too high and your lamp heads can actually explode! Also, never replace NiCad batteries with Sealed Lead-Acid as they require completely different circuit boards due to their different charging requirements.
Batteries should only be replaced with the same type. There are three issues here when we are referring to type:
- Material composition (lead-acid vs. NiCad)
- Amperage capacity
The voltage and amperage need to be the same to insure that your lights will illuminate to the right brightness level and remain lit for the required 90 minutes of time. Too low a voltage will cause your lights to be dim; while too high a voltage will blow the bulbs. An amperage rating of less than the original will not insure that your lights remain lit for the full 90 minutes in a power outage situation.
Replacing lead-acid batteries with nickel-cadmium causes problems in that the charging circuit is different for the two. Lead-acid batteries typically recharge in 24 hours, while NiCads recharge in 3-1/2 hours. The two battery types are manufactured with different connections to aid in identifying them. Lead-acid batteries typically have screw terminals, while NiCad batteries typically have wires attached to them.
Call us today at 800-480-0707 for more information on emergency light batteries, to ask a question, or place an order. Representatives are standing by so please call today.