I am going to enjoy a san francisco to yellowstone by my own. My friends and would be with me and have decided to try this on our own. But the confusing thing is that I have just lost my power bank and am thinking of charging my phone with a car charger, but they are all getting hipper on me if the car battery gets low, then what will you do? They are not changing the car, battery, just shouting at me. Do share do you have any alternative to this problem?