I have a Coleman Hot Water On Demand System, the lowest tempature setting is still kinda warm. Water only comes out if you have propane hooked up with fuel in it, with the unit running.
If this is what you are referring to, this is the only battery powered system I know about made by coleman - I dont think that would be a good idea.
If you going to use it to water, I would look into a 12v water pump an put it on a timer.