What is required for storage batteries used in emergency lighting?

For storage batteries used in emergency lighting, the requirement to maintain 85% of charge for 90 minutes is critical because it ensures that the lighting system will be functional during a power failure for an adequate duration. This standard helps to guarantee that emergency personnel and evacuees have sufficient illumination to navigate safely during emergencies, such as power outages, fires, or other hazardous situations.

The specified percentage and duration—85% for 90 minutes—demonstrate a balance between the battery's ability to deliver power and the practical needs of safety standards. Emergency lighting systems are designed not only to provide light but to do so reliably over a set period, ensuring compliance with safety regulations and best practices.

This requirement aligns with standard testing and performance criteria in many codes and regulations, which are set to ensure that emergency lighting systems are both effective and trustworthy. In contrast, the other options either set unrealistic expectations for battery charge or misinterpret the typical requirements for emergency lighting.