A wireless power system includes a wireless power transmitting device such as a wireless charging mat for charging devices such as a cellular telephone and an earbuds battery case. The earbuds battery case receives earbuds and charges the earbuds from a battery. The wireless charging mat supports bidirectional in-band communications between the cellular telephone and the earbuds battery case. The earbuds battery case provides the cellular telephone with information on the battery charge level associated with the battery in the earbuds battery case and a battery charge level associated with each earbud in the earbuds battery case. The cellular telephone receives battery charge level information through the wireless charging mat and displays corresponding indicators. The earbuds battery case has a visual output device such as a light-emitting diode that is illuminated to indicate that the earbuds battery case is being charged.