After some recent fires...
QuoteAs of March 1, passengers on all South Korean airlines must keep their portable chargers within arm's reach and out of overhead bins.
Other airlines in Asia have added similar restrictions
QuoteIncidents involving lithium-ion batteries on U.S. airlines have been increasing. There were 84 last year, up from 32 in 2016. These included cases — in the cabins of both passenger and cargo planes — where batteries caught fire, emitted smoke or overheated. Portable chargers were the biggest culprit in these incidents, followed by e-cigarettes, according to the F.A.A.
https://www.nytimes.com/article/portable-batteries-fires-planes.html