I have seen rechargeable battery powerd AC power inverters at wholesale clubs like SAM's or Costco. Not sure of the power capacity, or if safe to use in a confined space. Should have enough power for small appliances, or some types of heaters. I know that a discharging car battery gives off combustible fumes. Perhaps could be placed on a balcony, or that their design uses a different type of battery that is safe for indoor use. Regards, Keys