A hearing aid having a rechargeable battery and a charger for charging the battery includes a first microphone and a first speaker in the hearing aid and a second microphone and a second speaker in the charger for acoustically transferring data between the hearing aid and the charger. The hearing aid can detect the charge state of a battery and send a signal to the charger indicative of the charge state. The charger also includes a chamber for receiving at least a portion of the hearing aid.