Heating from a battery is not a good solution. Electric heat just takes way too many watts. 100 amp*hour battery x 12 volts = 1200 watt*hours. Keep the battery above 50% for long life and that leaves you 600 watt*hours available to use. You could run a 1500w heater for maybe 15 or twenty minutes before you'll need to recharge the battery.
A small propane catalytic heater is probably best. You can get a Mr. Buddy heater with an adapter hose to run it from a standard 5g propane tank, which you can then get filled at a propane distribution house.
Where I live, the 5g trade-in deal they have all over town costs $30 for a 5g bottle of gas, whereas the local propane house (NOT the local U-Haul shop - this is the place that runs the trucks that deliver to the local U-Haul shop) charges about $2 per gallon to refill a tank (5g minimum purchase and the "yard price" varies from day to day, lately it's been running between 1.80 and 2.20).
A catalytic propane heater will consume the oxygen in the living space, so you need to provide fresh air when using it. This is a non-issue however, since two humans breathing will consume the oxygen as well - so you MUST provide fresh air anyway.
Last edited by dwh; 01-22-2011 at 08:10 PM.
Current: 76 E-250, bubble-top, self-contained|couple of old Yamaha enduros
Previous wheelers: 41 Willys|78 FJ40|78 Bronco|84 Bronco|74 Ramcharger|78 Ramcharger|79 D150 PowerWagon|77 D100|79 D400 dually, converted to 4WD, utility bed, 10' Lance|75 Westy|69 Scout, RHD|bunch of others|bunch of bikes|couple of boats|couple of motorhomes|blah blah|so what|not my idea|just doin' what I'm told|wank wank|this space for rent|candy is dandy|but liquor is quicker