"If, when asked to do so, you are unable to demonstrate that your device has power you will not be allowed to fly on your planned service," the airline statedon its website.
On Sunday, the TSA announced travelers on direct flights to the U.S. could be asked to turn on their cellphones before boarding. That announcement followed an an earlier one from U.S. Homeland Security Secretary Jeh Johnson; the secretary said security for U.S.-bound flights would increase.
The TSA had said that cellphones and other devices that could not be powered on would not be allowed on flights, but British Airways' announcement takes the restriction a step further.
Travelers who are denied boarding because of a powerless device would be rebooked, according to the airline.
British Airways recommended fully charging devices before arriving to the airport, warning of limited charging stations at British airports. The airline also stated travelers on long-haul flights passing through the UK should be careful of depleting their devices early in their trip.