In an indication detection system, a battery data acquisition unit is configured to acquire battery data including current data, the current data being obtained by periodically measuring a current flowing through a battery pack. A determination unit is configured to, when the current data in a charge period of charging the battery pack by a charger include a section temporarily having a current value of zero and an integrated value of current in the charge period including the section temporarily having the current value of zero is larger than at least one of an integrated value of current in a discharge period immediately before the charge period and an integrated value of current in a discharge period immediately after the charge period, determine that the occurrence of the section having the current value of zero is an indication of the battery pack becoming unusable.