Batteries in Fire Alarms, Emergency Lights and Exit Signs
When they expire, how often to replace them, and which test decides it

Go look at the date on your batteries

Open the fire alarm panel and look at the two batteries sitting in the bottom of the cabinet. Somewhere on each one there should be a month and a year. Now walk to the nearest emergency light, press its test button, and ask yourself when that battery went in. Then do the same at the exit sign over the stair door.

The fire alarm battery has a date the code requires. Emergency lights and exit signs have a test the code requires, but no date. And all of them fail the same way: not all at once, but a little every month. The light still comes on when you press the button. The panel shows no trouble. Then the power goes out, and the battery that looked fine runs flat long before it should.

A battery does not die. It fades.

Every rechargeable battery loses capacity as it ages. It still takes a charge, it still shows the right voltage on the charger, and it still lights the lamp when you press the test button. What changes is how long it can keep going. A lead-acid battery is treated as worn out once it can deliver only 80 percent of its rated capacity, which is why the 2022 edition of NFPA 72 sizes fire alarm batteries with a 1.25 aging factor: the battery has to be big enough on its last day, not its first.

That is the trap. A quick test uses a small part of the charge, so a battery that has lost half its capacity still passes it. The only test that finds a tired battery is one that runs it for the full time it has to work in a real outage: 1½ hours for an emergency light, and a load test for a fire alarm panel. Heat makes it worse. Battery makers state that life is roughly halved for every 10 °C (18 °F) above room temperature, so a unit in a hot stair or mechanical room wears out years early.

So the two habits that matter: write the install date on every battery, so you know how old it is, and run the full-length tests, so you know what it can still do.

Fire alarm batteries: the date the code requires

A fire alarm panel must have a secondary power supply that runs the system for 24 hours in normal standby and then 5 minutes in full alarm (NFPA 72 §10.6.7.2.1). In almost every building that supply is a pair of 12-volt sealed lead-acid batteries in series, the same valve-regulated (VRLA) type used in alarm power supplies, annunciators and booster panels.

The date marking

Every storage battery is marked with the month and year of manufacture. If the manufacturer did not mark it, the installer finds the date code and writes it on (§10.6.10.1). That date is the starting point for everything else, and a battery with no readable date is a finding on its own.

A fire alarm power supply with its door open. The two 12 V standby batteries in the bottom of the cabinet are not a matched pair: one is a 7 Ah sealed lead-acid battery, the other a different make, and neither shows an installation date or a current test date. Nobody could say how old they were, when they were last tested, or when they are due. Batteries in a series string are replaced together, same size and same date. Field photo from an environment-of-care round.

The 2022 edition goes one step further. The installer also labels each battery with a replacement date no more than 4 years after installation, and from January 1, 2024 rechargeable batteries must be listed or recognized by a testing laboratory. The committee’s reason for the four years was simple: that is the replacement cycle the battery manufacturers recommend. The 2022 edition also changed the battery calculation, replacing the old 20 percent margin with a 1.25 aging factor, because a lead-acid battery is at end of life once it drops to 80 percent of its rated capacity.

The tests, and why the edition matters

Which test schedule applies depends on which edition your building is held to. That is not a small detail: in Georgia the fire marshal enforces NFPA 72-2022, while CMS and The Joint Commission hold hospitals to NFPA 72-2010 through NFPA 101-2012.

What shortens battery life

• Heat. Battery makers state that life is roughly halved for every 10 °C (18 °F) above normal room temperature. A panel in a hot mechanical room or an attic will not see four years.
• Deep discharge. A long power outage that runs the batteries flat, or a charger fault, does permanent damage. Test after any long outage.
• Shelf time. A sealed lead-acid battery loses a few percent of its charge every month in storage. A spare that sat on a shelf for two years is not a new battery. Check the date before you install it.
• Mismatched pairs. Replace both batteries in a series string together, with the same size and date. Why that matters is below.

Why a mismatched pair is a problem

A fire alarm panel runs on 24 volts, so its two 12-volt batteries are wired in series. The same current runs through both, in and out. That only works when the two are alike. If one is smaller, older or a different make, it empties first during an outage while the other still has charge, and the panel’s run time drops to whatever the weaker battery can give. On the charger it goes the other way: one battery fills before the other, so one ends up overcharged while its partner stays undercharged, and both age faster. Power-Sonic’s technical manual is blunt about it: do not mix batteries of different capacities, ages or makes in a series string.

Is there a code for it? Not a sentence that says “matched pair”. But NFPA 72 requires system components to be installed, tested and maintained according to the manufacturer’s published instructions (§10.3.2 in the 2013 edition), and the battery maker’s instructions say not to mix them. The panel was also sized for a battery of a stated type and capacity in its battery calculation; a smaller or tired battery in the string means that calculation no longer holds. And the 2022 edition requires rechargeable batteries installed from 2024 on to be listed or recognized. A mixed pair is a finding. Replace both, same type, same capacity, same date.

Swelling, cracked cases, leaking and corroded terminals mean replace now. You do not need a meter to see any of them. More on sizing and load testing is in Fire Alarm Batteries & Standby Power.

Emergency lights: the test the code requires, not a date

The Life Safety Code does not put a date on emergency light batteries. It puts a test on them instead, and the test is what retires a battery (NFPA 101 §7.9.3):

• Monthly: a functional test of at least 30 seconds, with tests 3 to 5 weeks apart.
• Yearly: a test of at least 1½ hours for battery-powered units. The light must stay lit for the whole test.
• Records: written, kept by the owner, available to the AHJ.

The 90-minute test is the one that finds tired batteries. A battery that can light a lamp for 30 seconds may die at minute 40. That is why the annual test has to be run for the full duration, with someone walking the building at the end to see which units are still lit.

Self-testing units

For existing battery lights the 2012 edition adds one more line: they must use reliable rechargeable batteries with a way of keeping them properly charged (§7.9.2.6). A unit whose charger has failed is running down every day, even though nothing looks wrong.

Self-testing or self-diagnostic units run the monthly test on their own and show a fault light when they fail. Under the 2012 edition staff still look at them every 30 days and the annual 1½-hour test is still done and written down (§7.9.3.1.2), even on units that run a 90-minute test of their own. Only computer-based systems that run the test and keep a test and failure history take the annual test over (§7.9.3.1.3). Read the product sheet before you count on the unit for the annual test: one widely used self-testing exit sign runs a 1-minute test every 30 days and a 30-minute test at 6 and 12 months. That is not a 90-minute test.

How long the batteries last

It depends on the chemistry, and the figures come from manufacturers, not from the code. Sealed lead-calcium packs are commonly sold with warranties of one to three years; nickel-cadmium units are often rated around 10 years of service life. A warranty is not a service life, so write the install date on every replacement battery and let the annual test tell you when it is done.

Exit signs with a battery

An exit sign with a battery is tested the same way as the emergency lights: 30 seconds monthly, 1½ hours yearly (NFPA 101 §7.10.9). The 2012 edition also requires the light sources of every exit sign to be looked at at least every 30 days. The 2024 edition dropped that separate sentence, but CMS still enforces 2012, so in a hospital the 30-day check stays.

The monthly test in practice: press and hold the test button and the sign should stay lit on its battery. This weatherproof sign over a parking deck stair door failed. The battery could no longer carry it, and in a power cut that stair would have lost its exit sign. Field photo from an environment-of-care round.

An LED exit sign almost never needs a new lamp, so it is easy to forget it has a battery at all. It does, and it ages exactly like the battery in an emergency light. The sign looks perfect every day until the day it has to run on its own.

How to test them properly

Press the button once, the light comes on, done? No. That only proves the bulb and the switch work. The battery has not been asked to do anything yet. Here is how the monthly and annual tests are meant to be done, on the units most buildings have.

Units with a plain test button

• Hold it, do not tap it. On a unit with no self-test, the light stays on only while you hold the button and goes off when you let go (Lithonia ELM2 instructions). The monthly test is at least 30 seconds (NFPA 101 §7.9.3.1.1), so count it out.
• Watch the whole 30 seconds. The lamps must stay fully lit for the entire test. A unit that starts bright and fades, or goes out at 20 seconds, has failed.
• Space the tests 3 to 5 weeks apart, and write down the date, the unit, the result and who did it.
• The annual test is 1½ hours, which nobody does with a finger on a button. The usual way is to switch off the normal power to the units for the full time, then walk the building at the end and see which ones are still lit. Plan where people will be first: the area has little or no emergency lighting for up to a day while the batteries recharge.

Self-testing units: the button does different things

On self-testing units one press usually starts a short timed test, and you do not have to hold it. The way to start the longer tests is not the same from one maker to the next. These come from each maker’s own instruction sheet:

Before and after the test

• Let it charge first. Most of the makers above ask for 24 hours on normal power after installation, and after a power failure, before a test counts (Dual-Lite says several hours). A 90-minute test run the morning after an outage can fail a good battery.
• Let it recharge after. After the 90-minute test the battery needs time to come back (Sure-Lites asks for 24 hours). Do not run the annual test the day before a storm or a survey.
• Learn the status light. Each maker has its own code. On the Lithonia SDRT option solid green means charged, one red flash a battery failure, two a lamp failure and three a charger failure; on Compass units two red blinks mean battery failure. A red light is a failed test even if nobody pressed the button.
• Exit signs follow the same rules. A battery exit sign is tested like an emergency light, monthly and yearly (§7.10.9), and self-testing exit signs use press sequences like the ones in the table. Check the sheet for yours.

In a hospital: what the surveyor writes

• K-0291 — emergency lighting, including the monthly and annual tests (NFPA 101-2012 §7.9).
• K-0293 — exit signs (§7.10).
• K-0345 — fire alarm testing and maintenance under NFPA 72, which is where missing or failed battery tests are written up.

Since January 2026 The Joint Commission files these under the Physical Environment chapter: emergency lighting and exit sign testing under PE.03.01.01 EP 3 and PE.04.01.01 EP 1, fire alarm testing under PE.04.01.01 EP 2. The record needs the activity, the date, the inventory, the frequency, who did it, the NFPA standard and the result. A test that was done but not written down is a test that did not happen.

The battery calendar

Check the edition your AHJ enforces before you write a finding. The fire alarm rows above follow NFPA 72-2019/2022; for CMS surveys use the 2010 table.

Writing it up