If a fire alarm system loses its primary power and the backup battery is fully discharged, how soon must the backup battery be fully recharged once power is restored?

• A. 24 hours
• B. 72 hours
• C. 96 hours
• D. 48 hours

Answer: (D)

When a fire alarm system loses power, the backup battery must be ready to take over if power is lost again. After the backup battery has been completely discharged, the system’s charger needs time to bring it back to full capacity. The rule in this context is that the battery should be fully recharged within 48 hours of power restoration. This window balances safe charging with keeping the standby power ready for the next outage, without risking overheating or damaging the battery. If the battery cannot reach full charge within 48 hours, it signals an issue with the charger or battery that should be addressed.

Shorter than 48 hours (for example, 24 hours) would be too aggressive for some battery chemistries and charging rates, while longer times (72 or 96 hours) aren’t required by the standard and could leave the system underpowered if another outage happens soon.