Japan's transport safety agency says a lithium ion battery on a Boeing 787 that overheated during an All Nippon Airways flight earlier this month, prompting an emergency landing, was not overcharged.

Japan Transport Safety Board chairman Norihiro Goto told reporters Wednesday the flight's data recorder showed the battery was not overcharged.

That contradicts an earlier finding by the agency as it investigates with the U.S. Federal Aviation Administration.

Investigators from both sides are probing the maker of the battery, GS Yuasa, and are examining it using CAT scans at a facility of Japan's aerospace agency.

U.S. investigators also said that they found no evidence of overcharging in a battery that ignited on a Japan Airlines Boeing 787 as it sat on the tarmac in Boston's airport. (AP)