Emergency light batteries
Batteries are the most common reason emergency lights and exit signs fail. Here is how to keep them healthy and catch failures early.
How emergency light batteries work
A battery-powered emergency light or exit sign keeps its battery charged from normal power. When power fails, the unit switches to battery and must run for at least 90 minutes. Common chemistries include nickel-cadmium (NiCd), nickel-metal hydride (NiMH), sealed lead acid and lithium iron phosphate (LiFePO4); each has its own lifespan, temperature tolerance and replacement part.
How long they last
Battery life depends on chemistry, temperature and how often the battery is cycled. Many emergency light batteries are replaced every few years, and units in hot spaces such as attics, mechanical rooms and warehouses age faster. Do not rely on age alone: the annual 90-minute test is what tells you a battery is done. See how long emergency lights last.
Signs a battery is failing
- The unit dims or shuts off before the end of a test
- A fault or battery indicator is lit
- The charging indicator is off while normal power is on
- Visible swelling, leaks or corrosion
Emergency light battery replacement
- Identify the exact replacement from the unit label or manual: voltage, capacity, chemistry and connector.
- Disconnect power to the unit following safe electrical practice.
- Swap the battery and secure the connector. Disconnected batteries after service are a common failure.
- Restore power and let it charge for the manufacturer's full charging time.
- Test and record: run the 30-second test (one press on One Touch units), and confirm normal status.
If the unit is old, discontinued or repeatedly failing, replacement with a self-testing unit removes manual testing going forward.
Catch weak batteries early
Self-testing GLS units run the 90-minute test every year automatically and the One Touch indicator flags low battery and improper battery connection, so problems show up on the next walk-through, not during an outage. See self-testing emergency lighting.
Frequently asked questions
How often should emergency light batteries be replaced?
Replace them when they fail the annual 90-minute test or show a fault, and plan for replacement every few years depending on chemistry and temperature.
Can I use any battery in an emergency light?
No. Use the battery specified for that unit (voltage, capacity, chemistry and connector) so the unit keeps its listing and performs as tested.