PROTECTING A BATTERY IN A BATTERY PACK

In a portable device, a load module includes a discharge switch for discharging a battery pack, and a detection circuit that detects a protection signal to control the discharge switch. A charge module includes a charge switch for charging the battery pack, and a detection circuit that detects the protection signal to control the charge switch. The battery pack includes a protection terminal that provides the protection signal, and protection circuitry that sets the protection signal to a state according to the battery pack's status. The protection signal turns the charge switch on and the discharge switch off if the protection signal is in a first state, turns the charge switch off and the discharge switch on if it's in a second state, turns the charge and discharge switches off if it's in a third state, and turns the charge and discharge switches on if it's in a fourth state.