I have a small unit like you describe that I connect to a stand alone battery for a little heat in remote situations.
The battery is a 12 Amp hour, and I carry two.
Using a larger amp hour battery would make more sense, but they cost money, and are bulky and heavy.
The scooter batteries are small in size, and weigh just 7 pounds.
I don't dare hook the heater into my onboard battery bank, for fear I'd fall asleep and drain them!
The setup works well, but each battery only provides heat for about an hour before it is done.
Not very practical, but the batteries were free, and it is much safer than an unvented propane heater.
My next step is to connect a spring timer in line to prevent the heater from running more than a few minutes when I fall back asleep...