All Nippon Airways Co. and Japan Airlines Co. announced Monday they have begun installing modified batteries into their grounded Boeing 787 Dreamliners.

ANA began swapping batteries in five jets grounded at Narita, Haneda, Okayama and Matsuyama airports, while JAL worked on jets at Narita and Haneda airports. ANA has 17 Dreamliners in its fleet, while JAL has seven.

According to ANA, each jet will take about five days to modify, and all 17 of its Dreamliners will be ready in about a month. It expects to start flying passengers in June after several weeks of test flights.