Take a look at this de-labeled smartphone Lithium-Ion battery:
Possibilities I thought of:
- Wireless charging - unlikely because the outer metal foil would screen the magnetic field, too short anyway
- Integrated active RFID tag - untypically short coil (not impossible though); same screening problem
- Thermocouple-like temperatur sensor - I think this is the most likely use because those batteries need temperature sensing
The battery is Samsung brand.