Why would a detached accessory building require two exits? For that matter, lights?
If it is a commercial building for dry boat storage then it would be classified as an S-1 structure, and the GC would need to worry about more than egress lighting only. If the building is classified as a U structure, two exits are required for more than 49 occupants.
Even if the building is considered an S-1, rather than a U, the code allows one exit for 29 or less occupants.
There are some assumptions that have to be made based on the information given. If the building is classified as an S-1 and the sq. ft. is over certain sizes then there are completely different requirements. Fire alarms being one.
Since the OP didn't mention the building having fire alarms and sprinklers which need electricity, I assumed it was a simple shed (detached structure) to house a boat or two.
If the building is completely enclosed with only one door the answer seems to be common sense or carry a flashlight.
Honestly, the simplest solution would be to call the AHJ and ask.:thumbsup: