Abstract: Various embodiments of modular battery authentication circuits are described. The various modular battery authentication circuits are intended to be utilized with electrically powered devices that do not comprise existing battery authentication capabilities. In one embodiment, a modular battery authentication adapter is described. The adapter comprises a housing in which a modular battery authentication circuit resides. One end of the adapter is positioned within a power input port of a device and a modular battery is positioned within the opposing end of the adapter. The authentication circuit within the adapter communicates with the modular battery to determine its authenticity before allowing the battery to power the device. A modular battery comprising an internal authentication circuit is also described. The modular battery is designed to interact with firmware stored within the device to determine whether the modular battery meets certain operational criteria.