You need to produce MSDS ( Material Safety Data Sheet ) for airline shipments to courier companies. Attached here the documents for two major wireless phones we are dealing. Cisco 8821 and Spectralink 8400 . Avaya no more supplying wireless phones .
Dect phones ( Yealink , Grandstream and Polycom ) generally use normal batteries that you can buy from supermarkets.
See the attached MSDS attachment.