Vinod Khosla, co-founder of Sun Microsystems and one of Silicon Valley’s most active cleantech investors through his firm Khosla Ventures, doesn’t always sound like a VC who has invested hefty sums in lithium-ion battery startups, including Sakti3 and Seeo. “Lithium-ion batteries are overhyped and will possibly be replaced,” he said today at the AlwaysOn Summit at Stanford. He told me after his talk, however, that Khosla Ventures is backing the technology because the “lithium-ion markets are here today. We’re investing because there are good markets.”

Problem is, costs have to down — or oil prices have to shoot up — for most battery ventures to make big winners of entrepreneurs and their investors, Khosla said. When asked during his talk this morning with Fenwick & West Chairman Gordon Davidson what it will take to get low-carbon cars on the road in significant numbers (which would boost demand for technology from companies like Sakti3), Khosla said, “The most important thing to remember is economic gravity — the cheapest thing ends up winning.” For that reaso