I agree with others who are pointing out how silly it is to be focused on this tiny load. Besides underinflated tires, there are factors such as vehicle speed, use of A/C, having windows or sunroof open, carrying loads on the roof, towing trailers, and several other much bigger ways to consume more (or less) energy. But taking this to its logical extreme would say that we all should drive the tiniest cars we can and travel at very low speeds -- go back to the 55 mph national speed limit of the 1980s? The solutions need to be much more global than charging a cellphone!