Investigators in Japan and the U.S. are still at a loss as to what caused the lithium-ion batteries on several of Boeing's 787 Dreamliner's to malfunction, causing fires and forcing the whole fleet to be grounded for an indefinite period of time. A day after Japanese regulators confirmed overcharging hadn't caused the problems, the U.S. National Transportation Security Board (NTSB) gave a press conference confirming only the known facts, namely, that there had been a fire and that they will continue investigating the incident around the clock.