In general, the disclosure relates to implantable medical devices including rechargeable power sources. In one example, the disclosure relates to a device including a rechargeable power source, a recharge module configured to recharge the rechargeable power source via inductive energy transfer, a posture state sensor configured to generate posture sensor data; and a processor. The processor may be configured to determine recharge coupling efficiency during a recharge session, receive posture sensor data generated by the posture sensor during the recharge session, and associate the recharge coupling efficiency determined during the recharge session with the posture sensor data.