Hybrid Tinkerers.Sff Cajc803 20050815151155 It looks like a typical Toyota Prius hybrid, but in the trunk sits an 80-miles-per-gallon secret – a stack of 18 brick-sized batteries that boosts the car’s high mileage with an extra electrical charge so it can burn even less fuel. Gremban, an electrical engineer and committed environmentalist, spent several months and $3,000 tinkering with his car. Link.