Upvote:2
For Lithium batteries with more than 100 watt hours (no date on page)
Says:
Lithium batteries with more than 100 watt hours may be allowed in carry-on bags with airline approval, but are limited to two spare batteries per passenger. Loose lithium batteries are prohibited in checked bags.
So checking with the airline beforehand would be needed if > 100 Watt.
The Top Five Items People Ask About:.. , Batteries,.. (2018-08-07)
Consumer-sized lithium ion batteries [no more than 8 grams of equivalent lithium content or 100 watt hours (wh) per battery]. This size covers AA, AAA, 9-volt, cell phone, PDA, camera, camcorder, Gameboy, and standard laptop computer batteries.
If less than 100 Watt seems to be generally allowed for Carry-On-Baggage.
No meantion that a corresponding Laptop must exist.