Sure, airlines can have whatever policies, but while not adhering to them might get you into trouble with the airline, it’s not a legal issue. The TSA doesn’t get powers from that to do anything that they weren’t allowed to do otherwise.

Now, they might lie to you to get you to give them more than they’re entitled to, but that’s a different issue.

You’re allowed to have devices with lithium batteries in checked bags.

When portable electronic devices powered by lithium batteries are in checked baggage, they must be completely powered off and protected to prevent unintentional activation or damage. Electronic devices capable of generating extreme heat, heating elements must be isolated which could cause a fire if activated, by removal of the heating element, battery or other components.

https://www.faa.gov/hazmat/packsafe/printable-chart