An extra-corporeal controller unit for an implantable ventricular assist device (VAD) includes control circuitry integrated with a rechargeable power source without including any power cables between the control circuitry and the rechargeable power source. The rechargeable power source includes two or more rechargeable batteries configured in respective battery modules. The battery modules are configured for removable installation in a housing of the controller unit. Mating power connectors are integrated in the battery modules and the housing. The mating connectors are configured to couple each battery to the control circuitry whenever the respective battery module containing the battery is installed in the housing. An energy storage unit may be permanently included in the controller unit and configured to remain fully charged and provide power to the VAD when the battery modules are removed.
