An exit sign with battery backup uses normal building power every day and automatically switches to an internal rechargeable battery during an outage. Many commercial fixtures are designed for 90 minutes of emergency operation after a full charge, but the required runtime and product rating must be confirmed for the specific fixture and installation.
Battery backup is different from a battery-powered sign that operates without hardwiring. Most battery-backup exit signs are connected to AC power so the sign stays illuminated and the battery remains charged.
How exit sign battery backup works
- Normal operation: AC power illuminates the sign and the internal charger maintains the battery.
- Power failure: The transfer circuit automatically switches the fixture to battery operation.
- Emergency operation: The battery powers the EXIT legend and, on combination units, may also power the emergency lamp heads.
- Power restoration: The fixture returns to AC operation and begins recharging the battery.
This automatic transfer is why a hardwired sign can continue marking an exit route when normal lighting is unavailable.
How long does an exit sign battery backup last?
There are two different time periods to consider:
- Emergency runtime: how long the battery powers the fixture during a single outage. Many listed commercial products specify at least 90 minutes after a full charge.
- Battery service life: how many years the rechargeable battery remains usable before it can no longer hold sufficient capacity. Service life varies with battery type, temperature, charging conditions, test frequency and age.
A battery can still illuminate the sign during a brief test but fail before completing its required emergency duration. That is why both routine functional checks and any required duration tests matter.
When is battery backup needed?
Battery backup is commonly used where an exit sign or emergency light must remain operational after normal power is lost. Examples can include exit doors, corridors, stairs, assembly spaces, retail areas, offices, warehouses and other parts of an emergency egress path.
Requirements vary by project and jurisdiction. Confirm the approved plans, applicable codes, product listing and direction from the authority having jurisdiction rather than selecting a fixture based on runtime alone.
Types of battery-backup egress fixtures
- Exit signs: illuminate the EXIT legend during normal and emergency operation.
- Emergency lights: use one or more lamp heads to light the egress path during an outage.
- Combination units: combine an EXIT legend and emergency lamp heads in one fixture.
- Remote-capable units: can supply specified remote lamp heads when the unit has adequate rated capacity.
Compare battery-backup exit signs, emergency lights with battery backup and exit sign and emergency light combo units.
How to test the battery backup
Pressing the fixture’s test button simulates a loss of normal power. The sign should remain steadily illuminated from the battery, and any emergency heads should operate as designed. The test button is useful for a quick check, but a short test does not confirm full-duration capacity.
See How to Test an Exit Sign Battery With the Test Button for a step-by-step procedure and failure symptoms.
Signs the battery or fixture needs attention
- The sign turns off, dims or flickers when the test button is pressed.
- The emergency heads do not illuminate or are noticeably weak.
- The fixture passes a short check but fails a duration test.
- The charging or fault indicator shows an abnormal condition.
- The battery is swollen, leaking, corroded or unusually hot.
- The same failure returns after charging or maintenance.
A failed test can be caused by the battery, but it can also indicate a loose connection, faulty charger, damaged LED board, lamp-head problem or transfer-circuit failure.
What to confirm before buying a replacement
- Required emergency runtime and product listing
- Input voltage and wiring requirements
- Red or green legend and single- or double-face configuration
- Ceiling, wall or end mounting requirements
- Indoor, damp, wet or hazardous-location rating
- Whether emergency heads or remote-head capacity are required
If replacing only the battery, match the original voltage, chemistry, capacity, connector, terminal layout and dimensions. Do not assume that a battery fits simply because its voltage is the same.
Bottom line
Exit sign battery backup keeps a properly selected and maintained fixture operating when normal power fails. Choose the correct listed product for the space, test it according to the manufacturer and applicable requirements, and investigate any failure promptly. Continue with our Exit Sign Inspection Checklist or browse the Exit Sign and Emergency Lighting Learning Center.