Voltage detecting device, voltage detecting method, and battery pack system

A flying capacitor type voltage detecting method which uses a capacitor to detect a voltage of each battery stack of a battery pack which includes a plurality of battery stacks each of which includes a plurality of battery cells connected in series, comprising:

• charging the capacitor by making a current flow in a charging direction in a branch line which is a single line branched from a connection line connecting a
• detecting unit and each battery stack and connected to the capacitor;
• battery stack by the detecting unit;
• and
• discharging the capacitor by making a current flow in the branch line in discharging direction opposite to the charging direction.

A battery pack system comprising:

• a battery pack that includes a plurality of battery stacks each of which includes a plurality of battery cells connected in series;
• and
• a flying capacitor type voltage detecting device that detects voltages of the battery stacks by the capacitor,
• wherein the voltage detecting device includes
• a detecting unit that detects a voltage between both ends of the capacitor, as the voltage of each battery stack;
• and
• a branch line that is a single line which is branched from a connection line connecting each battery stack and the detecting unit and connected to the capacitor and where a current during charging of the capacitor and a current during discharging of the capacitor flow in opposite directions.