Why was another US-bound SWISS flight diverted due to an emergency?

Twice in the past two weeks, SWISS flights between Zurich and the United States have had to make emergency landings. Déjà-vuFast forward to August 9th, when another SWISS flight - this time from Zurich to Boston - had been en-route for three hours when smoke was detected in the cabin. From that date, power banks may no longer be used or charged during the flight. Charging the power bank itself from the aircraft’s electrical power supply is also now prohibited. This is what you should know before flying:READ MORE: Swiss flight passengers face new rules for taking power banks on planes