Failing the Emergency Light Duration Test? Here's Why It Cuts Out Early

TL;DR

• An emergency light that cuts out before the end of its duration test almost always means the battery has degraded and can no longer hold a full charge.

• Under BS 5266, every emergency light must run for its full rated duration (typically three hours) during an annual full discharge test. Dropping out early is a test failure, not a minor observation.

• The most common causes are battery age, a faulty charging circuit, and heat damage from being mounted near a heat source.

• In healthcare and other high-risk settings, a short duration failure is more serious because it shortens the safe evacuation window for people who cannot self-evacuate quickly.

• The fix is straightforward: isolate the unit, replace the battery or fitting, retest to the full duration, and log the finding and remediation against your fire risk assessment.

Introduction

If an emergency light drops out 30 or 45 minutes into a three-hour discharge test, the unit has failed and needs attention now, not at the next planned maintenance visit. This is one of the most common findings during annual emergency lighting testing, and it almost always comes down to a battery that can no longer hold enough charge to see out its rated duration.

For a healthcare estates team or compliance lead, that failure carries extra weight. Emergency lighting exists to guide people safely out of a building during a power cut or fire, and in a hospital, care home or other high-risk setting, some occupants cannot evacuate quickly. A light that only lasts a third of its rated time is a genuine gap in the escape route, not a technicality to note and revisit later.

This article explains exactly what an emergency light duration test checks, why units fail early, what BS 5266 requires, and what a Responsible Person should do the moment a failure is found.

Why Does an Emergency Light Duration Test Fail Early?

An emergency light duration test fails early when the battery cannot sustain the fitting for its full rated period, which is most commonly three hours for a standard non-maintained luminaire. The battery is the weak point in almost every emergency lighting system, and its capacity degrades steadily over its service life even when the unit appears to be working normally during quick monthly checks.

A monthly function test only confirms the light comes on. It does not reveal how long the battery can actually sustain that light, which is why the annual full duration test exists. A unit can pass every monthly check for a year and still fail its duration test outright, because charge capacity and simple illumination are two different things.

What Does BS 5266 Require From a Duration Test?

BS 5266-1 requires every emergency light to be tested to its full rated duration at least once a year, with most UK commercial and public buildings specifying a three-hour rating. During this test, the mains supply is disconnected and the unit must maintain adequate illumination for the entire period on battery power alone.

Alongside the annual full duration test, BS 5266 also requires a brief monthly function test to confirm each luminaire operates and self-test units are not showing a fault indicator. Both tests matter, but only the full duration test proves the battery still has genuine capacity, which is exactly what a short duration failure calls into question. For a full breakdown of what compliant testing looks like, see our guide to emergency lighting testing and BS 5266 standards.

If your unit is doing the opposite and staying lit long after the mains supply returns, that is a different fault with a different fix, covered in our guide to an emergency light that won't turn off.

Is This a Compliance Failure?

Yes. An emergency light that fails to reach its rated duration is a fire safety failure under the Regulatory Reform (Fire Safety) Order 2005, and it should be recorded as an action in your fire risk assessment the same day it is discovered. Emergency lighting forms part of the building's life safety systems, and an unrecorded or unresolved duration failure is exactly the kind of finding an enforcing authority looks for during an inspection.

The failure does not need to be dramatic to matter. A unit that manages two and a half hours instead of three is still a fail, because the standard sets a fixed requirement, not a rough guide. Partial performance is treated the same as no performance for compliance purposes.

Why This Matters More in Healthcare and High-Risk Settings

In a hospital, care home or other high-risk premises, evacuation is rarely instant. Patients who are bedbound, sedated, or reliant on staff assistance take considerably longer to move through a building than an able-bodied occupant, and a phased or partial evacuation strategy may extend the time escape routes need to stay lit. A duration failure that would be a same-day fix in an office becomes a more urgent safety gap in these environments, because the margin for error is already smaller.

This is also why healthcare and high-risk sector estates teams are often held to tighter internal testing and documentation standards than the BS 5266 minimum, with more frequent spot checks between the formal annual test.

What Causes Early Battery Drop-Out?

Most early duration failures trace back to one of three causes, and identifying which one applies determines whether a battery swap is enough or the whole fitting needs replacing.

Battery Age and Charge Cycles

Emergency lighting batteries, typically sealed lead-acid or NiMH cells, have a working life of around four to five years even with correct trickle charging. Every discharge and recharge cycle very slightly reduces total capacity, and once a battery drops below roughly 80% of its original capacity it can no longer reliably hold a full three-hour charge. Age-related decline is gradual, so a unit can go from a comfortable pass to a clear fail between one annual test and the next.

Poor Charging Circuit Performance

If the charging circuit is not delivering a full trickle charge between tests, the battery never reaches capacity in the first place, regardless of its age. This can result from a faulty charging PCB, a loose connection, or a unit that has been isolated at some point (deliberately or accidentally) and not properly reconnected. A charging fault produces the same symptom as a worn-out battery, so both need to be checked before assuming which one is at fault.

Environmental and Thermal Factors

Heat shortens battery life faster than almost any other factor. Emergency lights mounted close to heaters, boiler rooms, kitchens, or in poorly ventilated risers run hotter than the rest of the building, and sustained heat exposure degrades battery chemistry well ahead of its rated lifespan. If several units in the same area are all failing duration tests around the same time, the local environment is worth investigating alongside the batteries themselves.

What Should You Do Next?

The moment a unit fails its duration test, take it out of service as a reliable safety device and treat the finding as an open action, not a note for later.

1. Record the exact failure time (for example, "cut out at 45 minutes of a 3-hour test") against the unit's location in your emergency lighting log.

2. Isolate and inspect the unit to determine whether the charging circuit is delivering a proper charge before assuming the battery is at fault.

3. Replace the battery, or the full fitting if the unit is beyond its serviceable life or the charging circuit itself has failed.

4. Retest the unit to its full rated duration before signing it off. A partial retest is not sufficient evidence of a fix.

5. Update your fire risk assessment and emergency lighting log with the finding, the remedial action taken, and the retest result, so there is a clear compliance trail if an inspector asks.

How Often Should Emergency Lighting Be Duration Tested?

BS 5266 requires a full duration test at least once a year, alongside a brief monthly function test of every luminaire. Many facilities and healthcare estates teams choose to run additional spot checks between the annual test, particularly on units in high-heat locations or those with a known history of early failures, since battery degradation does not always wait politely for the next scheduled test. Our guide to seasonal emergency lighting checks covers why testing frequency often needs to flex through the year.

Keeping a simple internal record of previous duration test results (not just pass or fail, but the actual time each unit reached) makes it far easier to spot a battery in decline before it fails outright, rather than finding out during the test itself. A structured emergency light testing programme, run by a competent contractor, builds this record for you automatically.

Frequently Asked Questions

Why did my emergency light only last 45 minutes during the test?

The most likely cause is a degraded battery that can no longer hold a full charge, though a faulty charging circuit or heat damage can produce the same result. The unit needs isolating and inspecting to confirm which fault applies before it goes back into service.

Is a short duration test failure a fire safety breach?

Yes. Emergency lighting that does not reach its rated duration fails to meet the Regulatory Reform (Fire Safety) Order 2005 and BS 5266-1, and it should be logged as an open action against your fire risk assessment immediately, not left until the next scheduled visit.

How long should an emergency light last during testing?

Most UK commercial and public buildings specify a three-hour rated duration under BS 5266-1, though some smaller premises use a one-hour rating. Check your building's fire strategy or previous test certificates to confirm which rating applies to your installation.

Can I just replace the battery instead of the whole unit?

Often, yes, provided the fitting itself and its charging circuit are in good working order and the correct replacement battery is available. If the charging circuit has also failed, or the fitting is old and no longer supported, replacing the whole unit is usually the more reliable option.

How often does BS 5266 require a full duration test?

BS 5266-1 requires a full duration test at least once every twelve months, in addition to a brief monthly function test of every emergency light. High-risk premises such as hospitals often add extra spot checks on top of this minimum.

What happens if I ignore a failed duration test?

An unresolved duration failure leaves a genuine gap in your escape route lighting and is a Fire Safety Order breach that an inspecting officer can act on. It also removes any defence that reasonable steps were taken if the light was needed during a real evacuation and failed.

Do all emergency lights need a 3-hour duration test?

Most do, since three hours is the standard rating specified in BS 5266-1 for the majority of UK commercial and public buildings, but some premises use a one-hour rated system depending on their fire strategy. Always test to the duration stated on the fitting or in your building's emergency lighting design documentation, not an assumed figure.