Do hotels have back up generators?

Most do, in times of crisis or diaster they evict people but only when generators run out of fuel which is like 3 days or some just keep refueling them, schools, hospitals, hotels and fire stations and some gas stations are required to have them and nursing homes usually do too. I stayed at a Marriott once when the power was out for days in the winter when my home got cold and it was nice it felt normal and the most important thing was it was safe, also they may charge extra to your stay due to costs of fuel for the generators.