A tool battery pack can include a current detection element for detecting a discharge current or a charge current, a monitoring section for inputting a current signal of the discharge current or the charge current through the current detection element and for inputting voltage signals of each cell battery, and a control microcomputer for performing discharge control or charge control based on the signals from the monitoring section. Further, the tool battery pack is constructed such that the current signal through the current detection element is input to both the monitoring section and the control microcomputer.