Backup power units?

[marcingo]

I have heard of these. Basically I need something that will always be plugged into the wall that I can plug a powerhead and heater to. When the power goes out the powerhead and heater automatically run off this unit for a certain time. When the power comes back on it automatically charges the unit. I would like it to not be some giant generator. Is there such a thing out there and if so anyone know where I can get it and what its called? Thanks.