I posted this recently, in answer to a question JetBlue's policy for lithium batteries:
JetBlue operates to essentially the same rules specified by TSA. Devices with installed batteries (cameras, phones, laptops etc) are permitted in both checked and carry-on luggage, but spare (uninstalled) lithium batteries and power banks must be in carry-on bags only. Batteries must not exceed 100 watt-hours (Wh), though larger ones up to 160Wh may be allowed with prior approval.
Spare batteries must be protected from short circuit (original packaging, tape over terminals, or in separate bags).
Checked Baggage: Generally prohibited for spare, loose batteries, or power banks. Devices containing batteries may be checked if completely powered off and protected from activation.
Capacity Limits:
<100 Wh: Allowed in carry-on and checked (if in device).
100–160 Wh: Max 2 spare batteries allowed with approval.
>160 Wh: Generally prohibited.
Other airlines, both US and other countries, may have different restrictions which aren't necessarily the same as those specified by TSA. It's always wise to check with the airline you're flying with. Most have details in the FAQs on their website.