A system, comprising: at least two implantable devices (620,630) including a first implantable device configured for implantation at a first implanted location and a second implantable device configured for implantation at a second implanted location, the first implantable device including a first implantable device coil and a first charge storage device, and the second implantable device including a second implantable device coil and a second charge storage device; and an external system including at least two series-connected external system coils (612, 613) and a driver driving the at least two external system coils (612,613), the at least two external system coils including a first external system coil and a second external system coil, wherein the external system is configured to: transfer energy from the first external system coil in a first external position to the first implantable device coil of the first implantable device when implanted in the first implanted location in proximity of said first external position for use in charging the first charge storage device; and transfer energy from the second external system coil in a second external position to the second implantable device coil of the second implantable device when implanted in the second implanted location in proximity of said second external position for use in charging the second charge storage device, characterized in that the first and second implantable devices (620,630) are configured to detune the first and second implantable device coils (621,631), respectively, to independently control energy transfer from the external system. at least two implantable devices (620,630) including a first implantable device configured for implantation at a first implanted location and a second implantable device configured for implantation at a second implanted location, the first implantable device including a first implantable device coil and a first charge storage device, and the second implantable device including a second implantable device coil and a second charge storage device; and an external system including at least two series-connected external system coils (612, 613) and a driver driving the at least two external system coils (612,613), the at least two external system coils including a first external system coil and a second external system coil, wherein the external system is configured to: transfer energy from the first external system coil in a first external position to the first implantable device coil of the first implantable device when implanted in the first implanted location in proximity of said first external position for use in charging the first charge storage device; and transfer energy from the second external system coil in a second external position to the second implantable device coil of the second implantable device when implanted in the second implanted location in proximity of said second external position for use in charging the second charge storage device, characterized in that the first and second implantable devices (620,630) are configured to detune the first and second implantable device coils (621,631), respectively, to independently control energy transfer from the external system. transfer energy from the first external system coil in a first external position to the first implantable device coil of the first implantable device when implanted in the first implanted location in proximity of said first external position for use in charging the first charge storage device; and transfer energy from the second external system coil in a second external position to the second implantable device coil of the second implantable device when implanted in the second implanted location in proximity of said second external position for use in charging the second charge storage device, characterized in that the first and second implantable devices (620,630) are configured to detune the first and second implantable device coils (621,631), respectively, to independently control energy transfer from the external system.