Swappa requires all devices to meet certain criteria requirements in order to be listed for sale. One of the requirements is having a fully functional battery.
Swappa defines a fully functional battery as one that properly charges and discharges.
Additionally, if you are listing an iPhone for sale on Swappa, and the battery health is below
80% and an Apple battery message is showing in the settings, this must be disclosed on the listing.
Read more: Understanding Apple's Battery Health