Does using lithium batteries change the NFPA 72 sizing calculation itself?

The underlying standby-plus-alarm ampere-hour calculation and duration requirements (24 or 60 hours standby, 5+ minutes alarm) apply regardless of battery chemistry — what can differ is the appropriate derating factor and the specific available battery capacity sizes, both of which should be based on the specific lithium product's manufacturer documentation rather than assumed identical to SLA conventions.

Can an existing SLA-based fire alarm system be retrofitted with lithium batteries?

Only if the installed FACP is specifically listed by its manufacturer to support lithium battery charging and supervision — retrofitting a lithium battery into a system whose charging circuitry was designed and listed only for SLA is not a simple drop-in replacement and would compromise the system's listing and safe operation.

Is lithium always more expensive than sealed lead-acid for fire alarm applications?

Lithium batteries commonly carry a higher upfront purchase cost than comparable-capacity SLA batteries, but the comparison over the system's full service life depends on relative replacement frequency and labor cost for battery replacement — a full cost comparison should weigh total lifecycle cost, not just initial purchase price, though this analysis is separate from and doesn't override the fundamental listing-compatibility requirement.

Engineering·6 min read·August 14, 2026

🔌 Sealed Lead-Acid vs. Lithium Batteries for Fire Alarm Systems

How sealed lead-acid and lithium iron phosphate batteries compare for fire alarm control panel backup power, and what to check before specifying either chemistry.

By EngineersUniverse Editorial Team

Engineering Editorial & Technical Review Team

Published August 14, 2026

Why Battery Chemistry Choice Matters for Fire Alarm Systems

Sealed lead-acid (SLA, also called VRLA — valve-regulated lead-acid) has long been the dominant battery chemistry for fire alarm control panel backup power, but lithium iron phosphate (LiFePO4) batteries have become an increasingly available alternative supported by a growing number of FACP manufacturers. The choice between them affects service life, capacity retention over time, physical size and weight, and — critically for a life-safety system — has to be confirmed as compatible with and listed for use with the specific FACP model being installed.

Sealed Lead-Acid: The Established Default

SLA batteries have decades of established use in fire alarm applications, are widely available from multiple manufacturers in standard sizes, and are well understood by installers and AHJs (authorities having jurisdiction) alike. Their known limitations include the sulfation-driven capacity decline over service life (covered in the companion derating factor article), a relatively fixed replacement interval commonly around 4 years, and comparatively heavier weight per unit of stored energy compared to lithium chemistries — a real consideration for larger systems requiring substantial battery capacity, where SLA battery weight and physical footprint can become a meaningful installation factor.

Lithium Iron Phosphate: The Newer Alternative

LiFePO4 batteries generally offer a longer service life than SLA (commonly cited as a significant multiple of SLA's typical replacement interval, though the specific figure depends on the manufacturer and product), a flatter discharge curve (delivering more consistent voltage throughout discharge rather than SLA's more pronounced voltage droop as it discharges), and meaningfully lower weight for equivalent stored capacity. These are genuine practical advantages, particularly for larger systems or installations where reduced long-term maintenance/replacement burden and physical weight matter.

Why Listing and Compatibility Confirmation Is Non-Negotiable

Regardless of which chemistry offers better theoretical performance characteristics, a fire alarm battery has to be specifically listed for use with the exact FACP model it's paired with — UL 864 (the standard governing FACP listing) evaluates the panel together with its compatible battery options, and using an unlisted battery, even one with objectively excellent specifications, can void the system's listing and code compliance entirely. This is a stricter, more consequential requirement than simply choosing "the better battery" on paper — the battery has to be one the specific FACP manufacturer has actually validated and listed for that panel, not simply any battery of appropriate voltage and capacity.

Why Not Every FACP Supports Both Chemistries

Charging circuitry, voltage monitoring thresholds, and battery health/supervision logic differ meaningfully between SLA and lithium chemistries — a charging profile appropriate for SLA isn't automatically appropriate for lithium, and vice versa. This is why FACP support for lithium batteries is a specific manufacturer feature that has to be confirmed for the exact panel model being used, rather than assumed to be universally available — older panel designs or certain manufacturer product lines may only support SLA, while newer designs increasingly offer lithium as a listed, supported option.

Practical Guidance for Chemistry Selection

For most standard fire alarm system designs, particularly retrofits into existing FACP installations or projects using well-established panel models, SLA remains a safe, code-compliant, and thoroughly proven default choice. For new installations, particularly larger systems where battery weight, footprint, or long-term replacement/maintenance cost are significant project considerations, checking whether the selected FACP model offers a listed lithium option is worthwhile — but the decision should always be anchored in confirmed manufacturer listing compatibility for the specific panel, not a general chemistry preference applied without that verification.

Topics covered

SLA vs lithium fire alarm batteryLiFePO4 fire alarmfire alarm battery chemistry comparisonVRLA battery fire alarm