On Wednesday, the U.S. Department of Transportation and the
Federal Aviation Administration issued new rules designed to
protect air passengers from the potential dangers of lithium ion
batteries. The new interim final rule disallows lithium ion cells
and batteries in the cargo area of passenger airplanes. The rule
also sets new guidance for lithium ion batteries that travel on
cargo-carrying planes, specifying that they not exceed a state of
being 30 percent charged. […]
The FAA’s current fact sheet suggests that these batteries
should be carried in the passenger area and not checked, though it
doesn’t go as far as banning them outright.
I think it’s been up to individual airlines to police this. On American, they’ve been asking me for years whether my checked bags contain any lithium-ion batteries.