State of charge information for a wireless power transmitting device

A wireless power system may include power transmitting devices, power receiving devices, and power transmitting and receiving devices. During a configuration phase (e.g., when placed adjacent to another device), a battery-powered transmitting device may transmit information to the additional device that identifies a presence of the battery in the transmitting device. The battery-powered transmitting device may periodically report its state of charge to a power receiving device using in-band communication. The battery-powered transmitting device may report its state of charge before a power transfer phase (e.g., in the configuration phase) or during the power transfer phase. The battery-powered transmitting device may report its state of charge to the power receiving device in response to a state of charge query from the power receiving device. The power receiving device may display the state of charge of the battery of the power transmitting device.