All emergency lighting fixtures rely on an internal battery to supply power when building electricity fails. These batteries are rechargeable, must fully charge within 24 hours, and are required to provide at least 90 minutes of illumination during a power outage, as outlined by UL 924 and NFPA life-safety codes. If you’re still selecting fixtures, see our battery backup emergency lights for code-ready runtime.
Last updated: August 2025
Quick Picks
Choose Chemistry
- SLA: Best for steel/outdoor/hazardous units, high Ah capacity.
- NiCad: Compact/lightweight for thermoplastic, quick recharge.
Size for Runtime
- Match voltage (6V/12V/24V) exactly.
- Pick equal or higher Ah for remote heads/longer runtime.
Test & Replace
- Monthly push-button functional test.
- Annual 90-minute discharge.
- Replace with same chemistry and voltage.
Types of Emergency Light Batteries
- Sealed Lead-Acid (SLA) – Common in steel, outdoor, and hazardous location lights
- Nickel-Cadmium (NiCad) – Compact and ideal for thermoplastic models
Battery Comparison (Visual)
| Chemistry | Typical Voltages | Approx. Recharge | Strengths | Tradeoffs | Common Fixtures / Use Cases | Notes |
|---|---|---|---|---|---|---|
| Sealed Lead-Acid (SLA) | 6V • 12V • 24V | ~24 hours | Low cost, high Ah, rugged, wide temp range | Heavy/bulky, capacity fades with deep cycling | Steel emergency lights, wet-location/NEMA, hazardous location, remote-capable, Chicago steel combos | Float-charge friendly; ideal for long runtimes |
| Nickel-Cadmium (NiCad) | 3.6–9.6V packs (varies) | ~3.5 hours | Compact, light, charges fast, any orientation | Memory effect, cadmium recycling required | Thermoplastic emergency lights, slim exit signs, recessed/architectural combos | Stable in indoor temps; proven & cost-efficient |
| Lithium Iron Phosphate (LiFePO4) | Pack-dependent (≈6.4–12.8V) | ~2–4 hours | Long cycle life, thermally stable, lightweight | Higher cost; cold-weather may need heaters | Premium LED exit signs, edge-lit, slim emergency lights, lightweight remote-head systems | Needs BMS; verify UL 924 recognition |
| Lithium-ion (NMC/NCA) | Pack-dependent (≈7.2–14.8V) | ~2–3 hours | Very high energy density for tiny enclosures | Requires robust BMS & thermal management | Compact architectural fixtures, retrofit micro-packs | Some specifiers prefer LiFePO4 safety margin |
| Nickel-Metal Hydride (NiMH) | 3.6–9.6V packs (varies) | ~4–8 hours | Cadmium-free, higher energy than NiCad | Higher self-discharge; heat sensitive | Select exit signs and combo fixtures | Moderate capacity; check charger compatibility |
Sealed Lead-Acid Batteries
Most commercial emergency lights use SLA batteries due to their:
- Low cost
- High amp-hour capacity
- Reliable performance across a wide temperature range
Available in 6V, 12V, and 24V options, SLA batteries can power fixtures with remote heads or higher-wattage lamps. If your unit supports multiple lamp heads or extended runtime, selecting the right capacity battery is essential.
Which fixtures typically use SLA?
Sealed lead-acid packs are the workhorse for steel emergency lights, wet-location/NEMA-rated units, and many hazardous-location fixtures where durability and long runtime matter. You’ll find SLA in Chicago-approved steel exit/emergency combos, industrial corridor lights, and projects that require remote-capable operation with separate heads fed over low-voltage conductors. Their higher amp-hour capacity supports twin 9–12 W heads, extended 90-minute tests, or even longer runtimes for large egress paths. SLA tolerates wider temperature swings and continuous float charging typical of emergency systems, making it a good fit for mechanical rooms, warehouses, parking structures, and outdoor enclosures. Downsides include weight, size, and gradual capacity loss with deep cycling—but for rugged environments and high-lumen requirements, SLA remains cost-effective and widely specified.
The 6V 4.5Ah SLA battery is one of the most common emergency lighting batteries and is available for same-day shipping.
Maintenance & Testing
Modern SLA batteries are sealed and maintenance-free. During your monthly functional test, the battery’s performance is evaluated automatically. Annually, disconnect the battery and check voltage levels—fully charged batteries should exceed nominal voltage (e.g., a 12V battery should read 13.2V when fully charged).
Use a battery load tester rather than a standard multimeter for more accurate results under real-world conditions. A multimeter only shows resting voltage and may give false “good” readings.
Nickel-Cadmium Batteries
NiCad batteries are ideal for compact, thermoplastic emergency light units where space is limited. Their smaller size and lightweight construction make them perfect for low-profile, indoor use.
Which fixtures typically use NiCad?
NiCad packs dominate thermoplastic emergency lights and many budget-friendly LED exit signs because they fit into slim housings while providing dependable discharge curves. Typical applications include office corridors, classrooms, retail back-of-house, and multifamily hallways where ambient temperatures are moderate and maintenance teams value quick recharge (≈3.5 hours). You’ll also see NiCad in recessed or architectural combo units where weight must be kept low, and in fixtures with self-testing electronics that expect predictable NiCad charging profiles. Tradeoffs: cadmium requires responsible recycling, energy density is lower than modern lithium chemistries, and repeated partial testing before full recharge can encourage memory-effect behavior. For many indoor, low-profile fixtures, however, NiCad remains a proven, cost-efficient choice.
Advantages of NiCad Batteries
- Compact and lightweight
- Fast charge time (typically 3.5 hours)
- Mountable in any orientation
- Spill-proof and durable
NiCad emergency light batteries offer space-saving power in a compact form and are available for immediate shipping.
Maintaining NiCad-Powered Fixtures
NiCad batteries are sensitive to memory loss. Always allow them to reach full charge before testing. If a power outage drains the battery, let it fully deplete before recharging. Monthly push-button tests and an annual full 90-minute test ensure long-term reliability and compliance.
Other Battery Chemistries (Pros & Cons)
While SLA and NiCad are the most common in legacy and value-focused fixtures, newer emergency lights increasingly ship with other chemistries—each with distinct tradeoffs and typical use cases:
- Lithium Iron Phosphate (LiFePO4) — Pros: Long cycle life, stable chemistry, lighter weight, fast recharge, low self-discharge. Cons: Higher upfront cost; cold-weather performance can require heated packs. Common uses: Premium LED exit signs, slim edge-lit models, compact emergency lights, and some remote-head systems where weight matters.
- Lithium-ion (NMC/NCA) — Pros: Very high energy density for small enclosures. Cons: Requires robust battery management; thermal considerations; some specifiers prefer LiFePO4 for safety margin. Common uses: Specialty micro-packs in compact architectural fixtures and retrofit kits (always verify UL 924 recognition).
- Nickel-Metal Hydride (NiMH) — Pros: Cadmium-free, better energy density than NiCad. Cons: Higher self-discharge, shorter life at elevated temps. Common uses: Select exit signs and older combo models where moderate capacity is sufficient and reduced hazardous content is desired.
Whichever chemistry you choose, confirm that replacement packs are UL 924 recognized for the specific fixture and that charging electronics are compatible. Mixing chemistries without matching the charger profile can reduce runtime or damage components.
Battery Replacement Guidelines
Always replace your emergency light batteries with the same type:
- Chemistry: Never substitute SLA with NiCad or vice versa
- Voltage: Must match the original battery
- Amperage: Must be equal to or greater than the original capacity
Using mismatched batteries can result in:
- Underperformance (dim lights or insufficient runtime)
- Component damage (bulbs blowing or circuit board failure)
Can I Replace a Lead-Acid Battery with a NiCad?
In most cases, no. SLA and NiCad batteries use different charging circuitry. SLA batteries take about 24 hours to charge, while NiCads recharge in about 3.5 hours. Also, their physical connectors differ: SLA batteries typically use screw terminals, while NiCads are often hardwired.
Conclusion
Understanding which type of battery your emergency light uses is key to ensuring performance, safety, and compliance. Whether you’re outfitting a small office or an industrial facility, maintaining your batteries properly will help your emergency lighting system perform when it’s needed most.