TOKYO -- The joint U.S. and Japanese investigation into the Boeing 787's battery problems has shifted from the battery's maker to the manufacturer of a monitoring system.Japan transport ministry official Shigeru Takano said Monday the probe into battery maker GS Yuasa was over for now as no evidence was found it was the source of the problems. Ministry officials now will inspect Kanto Aircraft Instrument Co. as part of the ongoing investigation. It makes a system that monitors voltage, charging and temperature of the lithium-ion batteries.All 50 of the Boeing 787s in use around the world are grounded after one of the jets operated by All Nippon Airways made an emergency landing in Japan earlier this month when its main battery overheated. Earlier in January, a battery in a Japan Airlines 787 caught fire while the plane was parked at Boston's Logan International Airport.GS Yuasa shares jumped on the news it is no longer being investigated, gaining nearly 5 percent in Tokyo trading. The issue had plunged 12 percent after the battery problems surfaced in Japan.Ministry officials stopped short of saying that Kanto's monitoring system was under any special scrutiny, saying it was part of an ongoing investigation."We are looking into affiliated parts makers," Takano said. "We are looking into possibilities."Kyoto-based GS Yuasa declined to comment.Hideaki Kobayashi, spokesman for Kanto Aircraft, based in Fujisawa, southwest of Tokyo, declined comment. He said it was too early to tell whether its system was at fault.Last week, U.S. federal investigators said the battery that caught fire in Boston showed evidence of short-circuiting and a chemical reaction known as "thermal runaway," in which an increase in temperature causes progressively hotter temperatures.