In some examples, a medical device system includes a first implantable medical device. The first implantable medical device (IMD) may comprise circuitry configured to at least one of deliver a therapy to a patient or sense a physiological signal from the patient; generate stimulation deliverable to a patient; a first rechargeable power source; and a secondary coil coupled to the first rechargeable power source, the secondary coil configured to charge the first rechargeable power source via inductive coupling with a primary coil of an external charging device. The medical device system may comprise processing circuitry configured to control charging of the first rechargeable power source based on a charge state of a second rechargeable power source of a second IMD.