The device is powered by a 3.7V 250mAh Lithium Polymer battery

Length: 29mm

Width: 20mm

Thickness: 5.5mm

The battery had a PCB connected to it containing two components:

8205A 1011HC (5A 20V N-Channel MOSFET)

DW01 (Battery management IC)

This module protects the battery from over-charging and over-discharging, allowing a stable power supply to the device.