Abou the D'Addario PW-CR2032-04 Lithium Battery for Tuners, Pack of 4:
 
D’Addario CR2032 Lithium Batteries provide up to 3 volts of power and are intended for use with D’Addario tuners, Humidity Temperature Sensor, and other electronic devices. Using proven technology, these 3V lithium batteries provide longer life in most digital devices.