All 50 of the Boeing planes in service were grounded in mid-January after their lithium-ion batteries emitted smoke on several separate occasions.
The Federal Aviation Administration (FAA) said airlines needed to replace the batteries to return to service and it will publish a final directive next week.
Other international regulators are likely to follow but it will still be a couple of weeks before flights resume.
The FAA said it would closely monitor modifications of the aircraft and teams of inspectors would be sent.
The plane is the first in the world to use the lithium-ion batteries, which are lighter, hold more power and recharge more quickly.
Problems with the battery sparked a battery fire on a parked Japan Airlines 787 at an airport in Boston and another incident in which battery smoke forced an emergency landing of an All Nippon Airways 787 in Japan.
The grounding has cost Boeing an estimated $US600 million, while All Nippon Airways lost some 1.4 billion yen ($US15 million) in revenue through January's disruption alone.
