Charging and discharging system for electronic device

A charging and discharging system comprising:

• a first cell assembly comprising a first cell, a first connecting piece, and a second connecting piece;
• a second cell assemble comprising a second cell, a third connecting piece, and a fourth connecting piece;
• a circuit board comprising a positive end, a coupling end, and a grounded end;
• and
• a controller secured to the circuit board and configured for detecting a voltage U1 across the first connecting piece and the second connecting piece, and a voltage U2 across the third connecting piece and the fourth connecting piece;
• wherein the first connecting piece, a positive pole of the first cell, and the positive end are connected in series;
• the second connecting piece, a negative pole of the first cell, and the coupling end are connected in series;
• the third connecting piece, a positive end of the second cell, and the coupling end are connected in series;
• the fourth connecting piece, a negative end of the second cell, and the grounded end are connected in series;
• when the charge and the discharge system is charged, the controller stops the circuit board charging the first cell assembly and the second cell assembly when the voltage U1 or U2 is arrived to a highest voltage U200;
• and when the charge and the discharge system is discharged, the controller stops the first cell assembly and the second cell assembly discharging when the voltage U1 or U2 is arrived to a lowest voltage U100.