What percentage of full charge must a storage battery maintain for emergency lighting and power?

The requirement for a storage battery to maintain a specific percentage of full charge for emergency lighting and power systems is critical for ensuring reliability during power outages or emergencies. The correct answer, which states a battery must maintain a charge of 87.5%, aligns with standards that govern emergency systems, such as those set out by the National Fire Protection Association (NFPA) or similar regulatory bodies.

Maintaining a charge of 87.5% ensures that the battery is sufficiently charged to operate emergency lighting and power supports for the requisite time, typically for at least 90 minutes. This percentage strikes a balance that allows for the longevity of the battery while ensuring it can perform during an emergency—allowing sufficient time for safe evacuation or to sustain critical systems.

Other percentages, like 75% or 90%, may not adhere to the specific requirements for reliability and usability demanded for emergency situations. A full 100% charge, while seemingly optimal, may not account for factors such as battery aging, environmental influences, or fluctuations in energy demand, which could lead to reduced battery performance in critical moments if not regularly balanced or tested. Thus, the 87.5% standard provides a practical threshold for battery maintenance in emergency scenarios.