A system interface having an interface for dual battery packs provides for power up sequencing of battery packs and pack switching under the control of a host processor within associated system electronics. The host processor communicates with each battery pack via a pack interface that includes a single wire mode control signal and a single wire status signal. The mode control signal allows the host processor to control the operational mode of selector switches within the respective battery pack. The single wire status signal provides status information to the host processor regarding the state of the selector switches within the respective battery pack. The mode and status signals are multi-state signals that permit at least three states to be identified via the single wire interface. Selector switches are provided only in the battery packs. No selector switches are included in the system electronics to minimize voltage drops between the selected battery pack and the system electronics.