Nikola Tesla invented a device containing 4 batteries linked in some order I will present, that the 4 batteries somehow recharged themselves.
How is it possibile? That can’t be, you’ll say, since every science class taught in school denies there is any other law above the conservation of energy. Indeed. True as it can be. But they didn’t tell you one little thing: energy sources ar far more large by number than those teachers taught you. There in fact is only one source of energy, and that is the Universal Energy. From it, aside others, derives the electric energy, the movement of electrons that make the electric current.
So, skipping theory, Tesla used the fact that lead ions are heavier than electrons. Every circuit, in it transitory phase (from zero-volt to x volts) develops a much higher voltage applied on the negative side. This voltage (pile-up of electrons meeting the much heavier lead ions) is then normally distributed in the circuit. If you cut off the load and the source battery, all the voltage made by the electrons gathered at the negative side of the battery you want to charge, go in that battery. If you do that from 200 to 800 times per second, you can charge the destination battery (lead-acid) in a very short time (tens of minutes). By switching the batteries between them, you restart the process and reload the source battery.
There is a company (Electrodyne Corporation) who tested this ensemblement and for three years they fueled many devices, with no unusual damage to the batteries.
Now: if linking this to a Toyota Prius HV battery, what would the MPG be? Huh? Infinite, at low city speeds?
P.S. For more details look on the PDF attached here starting with page 25.