The battery compartment can have four standard AA batteries No.5 simultaneously, from left to right 1.2.3.4, including No.1.2 is Group A, Group 3.4 is Group B, Group A and Group B are series structure, at least one battery in each group to operate normally and the output current, battery box output voltage is the sum of the highest single battery voltage in Group A and the highest single battery voltage in Group B, and the output voltage needs to be controlled between 2.0V-3.5V.