From time to time the electricity goes out in our neighborhood, lasting from a few minutes to a day or two. With a very elderly in-law living with us, we need continuous heat. Our gas furnace is electrically operated. Does anyone know of a constantly chargeable battery that could automatically switch on the furnace in such a ***** outage? And lasting more than a day or two? Our stairlifts have batteries that will work for three days. We can do without electricity if need be for the rest of house, despite some food loss. We're looking for an option to a major external gas generator.