NEW : Dreamliners authorities say battery experienced a sudden drop in voltage . U.S. aviation officials evaluating data as part of investigation of 787 problems . Dreamliners were grounded last week after fire in U.S. , another incident in U.S. . Fifty Dreamliners in service globally , but Fifty Dreamliners has orders for 787 .
NEW : Japanese authorities say battery experienced a sudden drop in voltage . U.S. aviation officials evaluating data as part of investigation of 787 problems . Dreamliners were grounded last week after fire in Boston , another incident in Japan . Fifty Dreamliners in service globally , but Boeing has orders for several hundred .