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Last reviewed: 19 September 2026 · By the Dad‑Link Emergency Lighting Division
What Is a Central Battery System?
Most emergency lighting is self‑contained: each luminaire holds its own battery and looks after itself. A central battery system takes a different approach — one central battery and charger power many emergency luminaires at once, over dedicated fire‑resistant wiring. On loss of the normal supply, the central unit takes over and keeps the connected luminaires lit for the rated duration.
Central systems are common in larger or higher‑risk buildings: hospitals, data centres, large retail and offices, where having one serviceable battery plant is easier to maintain and monitor than hundreds of individual battery packs. The trade‑off is that a single system now carries the whole load — so its service and discharge testing is critical, and that is what the central battery service report documents.
The central battery service report is a companion to the standard emergency lighting certificates. Where the periodic certificate checks the installation as a whole, the service report drills into the central plant: the battery health, the charger, the alarms, and the all‑important discharge test.
CPS vs LPS — Two Central Systems
Both are central battery systems to BS EN 50171; the difference is size and power.
| CPS — Central Power System | LPS — Low Power System | |
|---|---|---|
| Scale | A whole building or large zone. | A single area or floor. |
| Power | No fixed upper limit — sized to the load. | Up to 1.5 kW rated output. |
| Typical use | Hospitals, large offices, retail, industrial. | Smaller commercial units, individual floors. |
| Servicing | Identical in principle — inspection, readings, an 18‑point checklist and a full‑duration discharge test. | |
Why Service It — and the Law Behind It
Under the Regulatory Reform (Fire Safety) Order 2005 (and the equivalent Scottish and Northern Irish legislation), the responsible person must keep fire safety equipment in efficient working order. For a central battery system that means more than the routine monthly and annual luminaire tests — the central plant itself needs servicing by a competent person, in accordance with the manufacturer’s instructions and BS 5266‑1 clause 13.3.2, with the results recorded.
Batteries are consumables. A lead‑acid or lithium battery bank degrades with age, temperature and cycling, and one day it will no longer sustain the rated duration. The only way to know is to discharge it under load and measure how long it lasts. A service that skips the discharge test is not a service — it’s a look.
The Discharge Test — the Heart of the Service
The discharge test proves the battery can still power the connected luminaires for their full rated duration. The system is put onto battery, under its normal load, and the time it sustains the required output voltage is measured. If the rated duration is 180 minutes, the battery must hold up for 180 minutes.
Two numbers decide the outcome:
- Duration achieved — how long the system sustained the load. Reach the rated duration and it passes; fall short and it fails.
- End‑of‑discharge voltage — the output voltage at the end of the test must still be within the luminaires’ operating range, allowing for cable voltage drop. A system can technically “run” for three hours while the voltage has sagged too low for the far luminaires to work properly.
In Lux Meter Pro, if you enter a duration achieved that is below the rated duration, the report warns you on the spot that the system failed the duration test and should be assessed unsatisfactory — so the result is never quietly recorded as a pass.
The Readings That Matter
A proper service captures a set of electrical readings that, together, show whether the plant is healthy.
| Reading | Why it matters |
|---|---|
| Mains supply voltage | Confirms the incoming supply to the charger is healthy. |
| Charger float voltage | The steady voltage that keeps a charged battery topped up. Wrong float voltage slowly cooks or undercharges the battery. |
| Charger boost voltage | The higher voltage used to recharge after a discharge. Must suit the battery chemistry. |
| Battery voltage on float | The resting battery voltage — a first indicator of overall health. |
| Battery voltage at end of discharge | The critical one: still within the luminaires’ operating range at the end of the test, allowing for cable drop. |
| Load current on discharge | Confirms the battery is delivering the expected load. |
| Ambient temperature | Battery life and performance are temperature‑dependent; a hot plant room shortens life. |
| Duration achieved | The headline result — time sustained versus rated duration. |
The 18‑Point Service Checklist
The checklist is grouped into four areas. Each item is marked satisfactory, a defect, or not applicable.
Location & environment
- Battery room or enclosure ventilation is adequate and unobstructed.
- Ambient temperature is within the battery manufacturer’s limits.
- Enclosure and fire‑resistant wiring are intact, secure and labelled.
Battery
- Cells and terminals are clean, tight and free from corrosion.
- No leakage, swelling, cracking or discolouration of cells.
- Electrolyte levels correct (vented cells only).
- Cell or block voltages recorded and within tolerance.
- Impedance or conductance readings recorded where the manufacturer specifies them.
- Battery age checked and replacement date recorded.
Charger & controls
- Charger float and boost voltages correct for the battery type.
- Automatic changeover to battery on mains failure operates.
- Deep‑discharge protection operates.
- Mains failure, charger fault, battery fault and earth fault alarms and indications operate.
- Output voltage at the end of discharge is within the luminaires’ operating range.
- Circuit protective devices are correctly rated and labelled.
Test & records
- Full rated‑duration discharge test completed and the duration achieved recorded.
- System recharged and all indications normal after the test.
- Log book updated and spares available.
Worked Example — a Failing Battery
A five‑year‑old CPS rated for 180 minutes is serviced. The visual checks are fine, alarms operate, charger voltages are correct. The discharge test is run under normal load. It sustains output for 142 minutes before the end‑of‑discharge voltage drops out of range — 38 minutes short of the rated 180.
What the report records:
- Duration achieved: 142 min against a rated 180 — the app flags this as a failed duration test.
- Overall assessment: Unsatisfactory. The connected luminaires cannot be relied on for the full three‑hour period.
- Defect recorded: “Battery bank no longer sustains rated duration (142/180 min). Battery replacement required. Interim: reduced reliance / standby arrangement until replaced.”
- Follow‑up: battery replacement scheduled; a re‑test after replacement will confirm the full duration is restored.
This is the value of the discharge test. On the visual checks alone the system looked healthy; only loading the battery revealed that it had quietly lost a fifth of its capacity — a fifth of the escape time in a real emergency.
Standards & References
- BS EN 50171:2001 — central power supply systems. The product standard for CPS and LPS central battery units.
- BS 5266‑1:2016 — clause 13.3.2 covers the servicing of central battery systems as part of the overall emergency lighting maintenance regime.
- BS EN 50172:2004 / BS 5266‑8:2004 — the testing and record‑keeping routine the service feeds into.
- The manufacturer’s instructions — always the primary reference for the specific battery chemistry, charger settings and service intervals.
Recording It in Lux Meter Pro
The same form is available on iPhone and iPad in the app, and in the browser through our Cert It web app.
Open a service report
Choose Central Battery Service Report, add the client and installation, and the visit type (routine, commissioning or fault).
Record the system
Enter the manufacturer, model, CPS/LPS type, rated output and duration, and the battery type, capacity, age and cell count.
Take the readings
Record the mains, charger and battery voltages, load current, ambient temperature and the discharge test duration achieved.
Work the 18 items
Assess each checklist item across environment, battery, charger and records. Mark satisfactory, defect or N/A.
Record defects
Log any defect with the action taken or recommended. The duration warning flags a short discharge automatically.
Assess, sign & send
Set the overall assessment, sign, and generate the PDF. Keep it with the emergency lighting log book.
Common Mistakes to Avoid
- Skipping the discharge test. Visual checks can’t reveal lost capacity. If you didn’t load the battery, you didn’t test it.
- Ignoring end‑of‑discharge voltage. A system can run for the full time with the voltage sagged too low for the far luminaires.
- Not recording ambient temperature. A hot plant room is quietly shortening the battery’s life; it belongs in the record.
- Passing a short discharge. Anything below rated duration is unsatisfactory — replace or repair, don’t rationalise.
- Forgetting the recharge window. Leaving the building on a flat battery after the test is a live safety gap.
- No battery age or replacement date. Without it, nobody plans the replacement before it fails.
Before You Issue — Quick Checklist
Frequently Asked Questions
What is a central battery system in emergency lighting?
A system that powers many emergency luminaires from one central battery and charger, rather than each luminaire having its own battery. On mains failure the central unit supplies the luminaires over fire‑resistant wiring. Central power systems (CPS) and low power systems (LPS, up to 1.5 kW) are covered by BS EN 50171.
What is the difference between CPS and LPS?
A CPS (central power system) is a larger central battery system serving a whole building or zone. An LPS (low power system) is a smaller central supply rated up to 1.5 kW, typically for a single area. Both are central battery systems to BS EN 50171 and are serviced the same way, with a discharge test proving the rated duration.
How often should a central battery system be serviced?
Beyond the routine monthly and annual emergency lighting tests, the central plant should be serviced per the manufacturer’s instructions by a competent person, with results recorded. The annual full‑duration discharge test proves the battery can still sustain the rated emergency duration, usually three hours.
What happens if the discharge test fails to reach the rated duration?
The connected luminaires cannot be relied upon for the full emergency period. Assess the system as unsatisfactory, record the defect, and replace or repair the battery without delay. After a full discharge the battery also needs its normal recharge period before it can provide the rated duration again.
What does a central battery service report record?
The system and battery details, the charger, mains and battery voltages, the load current and ambient temperature, the discharge test duration achieved, an 18‑point service checklist across location, battery, charger and records, any defects, and the overall assessment with the engineer’s signature.
Can I do this service on a phone or tablet?
Yes. Lux Meter Pro provides the full central battery service report on iPhone and iPad, and in the browser through Cert It. Enter the readings and checklist on site and generate a BS EN 50171 PDF to email or file with the log book.
Service Central Systems With Confidence
We build the central battery service report into Lux Meter Pro and our Cert It web app — readings, the 18‑point checklist and an automatic warning if the discharge falls short of the rated duration, all in a clean BS EN 50171 PDF. Your details, logo and signature are saved once and applied to every report.