That day has come. Today, every Prius hybrid car on the road carries with it about 10 pounds of lanthanum. And yet, most Prius owners don't even know they use this rare earth element every day. The metal in question is lanthanum, but what can we sayÂ­, rare earth elements get no respect. A big breakthrough in battery technology, nickel-lanthanum hydride batteries pack more power into a smaller spaceâthey're about twice as efficient as the standard lead-acid car battery.