Fire Alarm Battery Testing and Sizing

A practical guide for fire alarm technicians

Michael Ellis, Volt Verify Inc.

1. Introduction

Battery performance is critical to the reliability of every fire alarm system. When power fails, the batteries must seamlessly supply energy to maintain fire alarm system operation for required durations as required by the codes and standards. Understanding how to properly size, test, and maintain these batteries is essential for technicians performing inspections or verification in accordance with CAN/ULC-S536-19 and CAN/ULC-S537-19.

2. Standards and Requirements

In Canada, the standards CAN/ULC-S536 (Inspection and Testing) and CAN/ULC-S537 (Verification) define the framework for fire alarm system evaluation.

  • CAN/ULC-S536-19 details inspection and testing requirements, including specific procedures for verifying battery operability. It notes that the battery type used must be one recommended by the manufacturer.
  • CAN/ULC-S537-19 addresses verification of installation and performance to ensure systems are installed and function as designed, following CAN/ULC-S524 (Installation). While it does not focus on individual component specifications, it ensures the overall system meets design intent.

Understanding these distinct purposes helps technicians correctly apply the standards and document compliance.

3. Battery Sizing Fundamentals

Proper battery sizing ensures the system can meet standby and alarm duration requirements. While most modern panels include load data, verifying current draw in the field provides assurance of accuracy and real-world reliability.

Step 1: Determine the system’s standby current

Standby current is the operational load of the fire alarm system operation when it is not in alarm. It includes control panel electronics, detectors, modules, relays, and supervised circuits.

Step 2: Determine the alarm current

Alarm current is the operational load when the fire alarm system is in alarm, including notification appliances, relays, and power supplies at full output.

Step 3: Apply duration requirements

Most systems are required to operate for:

  • 24 hours in standby, followed by
  • An alarm duration specified by the National Building Code (NBC), typically ranging from 5 minutes to 2 hours.

While some buildings have emergency generators, technicians should not automatically reduce battery capacity based on generator presence. Generator sizing varies widely—many are only rated to supply emergency power for 2–4 hours—and incorrect assumptions can lead to undersized batteries. Always verify the generator’s capacity, load connections, and applicable ULC/NBC requirements before adjusting

Step 4: Calculate amp-hour capacity

Use this simplified equation:

I = Current and T = Time.

Apply a derating factor to account for temperature, aging, and component tolerance. The derating factor must be taken from the manufacturer’s published installation instructions, and this will typically fall in the 20–25% range.

ULC-S524:2024 introduces a 1.25 safety factor for battery sizing. While it is not yet adopted into the National Building Code, the Ontario Fire Code already references ULC-S524:2024.

Technicians should always ensure they reference the local codes and requirements applicable to their jurisdiction.

Step 5: Select the appropriate battery size

For example: If a system draws 0.15 A in standby (24 hours) and 1.8 A in alarm (30 minutes):

Adding 25 % derating factor (4.5Ah x 1.25 = 5.63Ah) → select a higher rated battery such as a 7Ah.

4. Testing Overview

Routine testing ensures that batteries will perform under real conditions. Fire alarm systems rely on the batteries’ ability to deliver full current output when AC power is lost.

It is important to test the batteries first, because battery testing must always be done on a fully charged battery. During alarm testing, most fire alarm control panels shut off battery charging while in alarm, which can lead to inaccurate test results if done afterward.

Technicians should:

  • Verify battery voltage under load.
  • Check terminal tightness and signs of corrosion.
  • Measure and record both standby and alarm currents.
  • Confirm the charger is operating properly, ensuring both the charging current and float voltage are within the manufacturer’s specifications.

5. Battery Condition and Testing Methods

5.1 Visual Inspection

Inspect batteries for swelling, cracks, corrosion, or leakage. If batteries show signs of damage or distortion, they should be replaced immediately. Fire alarm batteries must always be replaced in pairs.

5.2 Functional and Load Testing

CAN/ULC-S536-19 permits only three methods for testing standby batteries:

  1. Required supervisory load for 24 hours, followed by full-load operation.
  2. Silent Accelerated Test (refer to Annex C1 “New Silent Accelerated Test Method”).
  3. Battery manufacturer’s test method.

Note: “Intelligent/Pulse Load” battery testers are no longer allowed to be used.

Technician’s perspective

(i) The 24-hour method is highly disruptive and impractical. Leaving a fire alarm on battery power for that long is dangerous and requires fire watch. Sounding

(ii) The New Silent Accelerated Test method can be the most practical and representative. Annex C includes a diagram of the resistor-based setup. While the resistor can generate considerable heat that may cause burns or damage, commercially available testers can mitigate this risk and perform the procedure safely and efficiently. Technicians performing this test should have training and appropriate PPE (gloves, safety glasses, long sleeve shirts.)

(iii) With the large number of battery manufacturers, it is not feasible to source and apply each manufacturer’s individual test method — some sites contain multiple brands.

6. Replacement and Maintenance Practices

Even with proper testing, batteries have a finite life. Typical sealed lead-acid (SLA) batteries used in fire alarm systems last between 3 to 5 years, depending on environmental conditions.

According to CAN/ULC-S536:2024 Section 9.4:

“Replace the battery based on the manufacturer’s indication date code or the interval as recommended and documented by the manufacturer. Where there is no manufacturer’s documentation of battery service life, the battery shall be replaced within 4 years.”

This clause formalizes a long-standing industry practice, ensuring that aging batteries are proactively changed before reliability declines.

Best practices:

  • Always replace batteries in pairs to maintain balanced charging and performance.
  • Record installation date, voltage, capacity, and replacement date in inspection logs.
  • Label each battery or panel with the next required replacement date.
  • Dispose of batteries responsibly through approved recycling programs.

7. Documentation and Reporting

Proper documentation is essential for traceability and compliance. Every inspection or verification report should include:

  • Date and method of test performed.
  • Measured standby and alarm current values.
  • Battery make, model, capacity, and date code.
  • Measured voltage under load.
  • Technician name and signature.

Accurate records help establish maintenance history, support code compliance, and identify trends such as premature battery failure or abnormal current draw.

8. Troubleshooting Common Battery-Related Problems

  • Frequent battery trouble conditions: often indicate charger failure or degraded battery terminals.
  • Swollen batteries: typically caused by overcharging or exposure to high ambient temperature.
  • Low voltage after test: indicates aging cells or high internal resistance — replacement required.
  • Inconsistent battery life: can stem from mixed-age or mismatched pairs. Always replace both together.

9. Conclusion

Proper fire alarm battery sizing, testing, and replacement are vital to maintaining system reliability and code compliance. The Silent Accelerated Test method, when properly applied, provides a safe, repeatable, and effective way to confirm performance without the disruption or impracticality of a full-duration discharge test.

Personal note: I have been using the New Silent Accelerated Test Method for years and have noticed significantly fewer battery-related fire alarm service calls as a result.

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