Yes rangers will have a vehicle with them – this will almost always be a 4-wheel drive.
If you considered use of the car battery, keep in mind groups might be staying up to a week at a time camping at a site on Country so the car battery would likely be significantly drained over this time, depending on the power requirement and devices they would need to connect to. So it would need to be supplemented with another power supply. But I’m assuming when you mentioned heating up water this refers to drinking water or showering water when camping – but I’m not sure how this relates to one of our projects?
Can I ask what design project you have in mind for your question? If it relates to this thread on ‘4.3 Appropriate energy supply for vehicle washdown facilities’ then I don’t believe car batteries would be sufficient to rely on for this energy input for a vehicle washdown station, and there are risks you’d need to consider in case people drained their battery when washing down their car and then break down in remote areas. And, I’m not sure what the purpose of heating up water would be here.
Feel free to comment here again if you have further questions or wish to clarify anything, or start a new thread if this relates to a different project.
Hope that helps and best of luck,