The only battery operated heaters I've known of are the ones that you use in a car on a 12 volt system to help defrost the windshield.
I've never heard nor seen any type of battery powered heater for household use in an emergency or anything since an electric space heater would consume a lot of power and drain a battery really quick.
Electric space heaters that you plug into your wall use 1500 watts on the high setting and that's a lot of power.
And even then those electric heaters only really work to supplement existing heat sources and do a very poor job at trying to warm up or keep a room warm by itself.
A good way to have heat during a power outage would be to have a natural gas heater that requires no electricity such as a floor furnace or natural gas wall heater or even a wood burning stove with enough dry firewood to heat your home during a power outage.
If a battery powered space heater did exist it wouldn't put out much heat and you'd probably be better off without the hassle of it for what little heat it would give out.