The present invention discloses an inquiry system having a database and a first testing module as well as a memory unit, a second testing module and a maximum power efficiency control unit built in a power bank. In addition to the information exchange performed by the first testing module through an external computer, the built-in second testing can perform information exchange with a device to be charged (such as a handheld electronic device) directly. Meanwhile, the charging time of the power back can be reduced through the maximum power efficiency control unit.