Using an AA 1.5V 5# battery as power supply, you can make a call for as long as 30 minutes.
Output current: 30mA
Output voltage: 3V-6V
Maximum output voltage: 6V
There are 5 commonly used brands of mobile phone joints, also you can use designated joint (above 500)

It is made with glistening and water-proof material with internationally universal style and convenient to wear. It adopts globally agreed warning color: yellow and red, for identification in case of emergencies.