A deep cycle lead acid battery (typically used in marine applications) could
probably provide 125 W (10 amps from a 12 V battery) for 6 hours or so. Use
a 12 V heater or a 125 VAC heater through an inverter. You would charge the
battery at home between uses.

As other have suggested, a solar panel might work for trickle charging.


-Elliott Drucker