The time a fully charged power failure light stays operable during an outage depends on the light's battery capacity. On average, this is about 3 to 4 hours.
Check compatibility before you buy
While Power failure lights work in most standard light fixtures, there are some limitations. They may not work on dimmer switches, fixtures that include incandescent or halogen bulbs, or circuits with ceiling fans. It is important to check the manufacturer's specifications for compatibility with your specific fixtures before purchasing power failure lights.
Brands include Energizer LED Rechargeable Plug-in Flashlight and Ideal Security Inc. SK636 Emergency Power Failure Light.