Passengers on Southwest Airlines flights will soon be required to keep their portable chargers in plain sight while using them because of concerns about the growing number of lithium-ion battery fires in a new policy that other airlines may adopt.

The TSA already bans rechargeable and non-rechargeable lithium batteries for phones and laptops from checked baggage. Carry-on baggage is fine, but Southwest Airlines will soon require those chargers to be outside of all bags and visible while in use during the duration of the flight.