I sell a lot of computer parts on eBay, occasionally including batteries. I do always make sure to protect them well, but is it legal to ship them priority? That is what I usually do because I want to keep up my reputation as a fast shipper. I have heard stories of computer batteries exploding, and I really don’t want the FBI at my door.
Lithium batteries are considered dangerous goods. Contact the company doing the shipping and see what their requirements are.
The USPS has them listed under ‘Examples of items that may be mailable but have specific restrictions’.
Link (click on the ‘Restricted tab’): https://www.usps.com/ship/can-you-ship-it.htm
Other links suggest the restrictions may include that they must be part of a device that is packaged properly so that it can’t be turned on and is secure so that it won’t get bumped.
in the USA you can call the USPS or what shipper you are using and ask.
to be legal you may need original packaging and the outside of the package labelled as to contents. there are different details depending on cicumstance.
the package has to be noncrushable and the battery non-shortable.
you should get the details from the USPS.