Techniques of charging electronic devices involve directing electrical power from a first device to the battery of a second device in response to the first device being in a first state, and directing electrical power from the second device to the battery of the first device in response to the first device being in a second state. For example, in response to a connection being established between a first device (e.g., a tablet computer) and a second device (e.g., a monitor), a charger of the first device detects a state of charge of the battery of the first device and a state of charge of the second device.