A dynamic power control circuit is provided. The control circuit can detect the presence of the external power source as well as detect one or more conditions of the device. For instance, the control circuit can detect a voltage difference between a first node coupling a first power output and a system circuit and a second node coupling a second power output and the batteries. The control circuit can also detect the activation or deactivation of the external power source. Based on the inputs, the control circuit can cause the controlled resistor to dynamically adjust a level of impedance between the first node and the second node. The controlled impedance between the first node and the second node enables the system circuit to dynamically utilize power supplied by the external power source as well as power supplied by the batteries.