I don't think you can ship Lithium batteries anymore by the Postal office. Last time I was there they ask whats inside and if its a battery, its rejected.
So you can't use USPS to ship laptops or phones?
I think its only if its the battery itself.
You cannot ship the unprotected cells, meaning the positive and negative contacts must be unexposed and unable to make contact with anything. Laptop batteries are inside a hard plastic case so if the packaging was damaged there is still no way a contact from a cell can connect with anything that could cause it to short and explode. I get batteries via USPS monthly and have never had a problem yet except when I ordered 20 Panasonic ncr18650b cells directly and they tried to ship them as just batteries. The shipment was seized at on of the sort facilities.