Abstract: The invention contemplates a cast-embedable coil structure which includes a single connector fitting, designed for exposure externally of a completed cast and for removable mounting and electrical connection to a self-contained light-weight rechargeable portable signal-generator unit. The signal-generator unit is mounted to the cast only for periods of therapeutic treatment, and it is removably mounted to a less-portable charging unit in intervals between periods of therapeutic treatment. The same connector fitting on the generator unit (a) establishes all necessary electrical connections for therapy when mounted to the cast fitting and (b) establishes all necessary electrical connections for recharging when mounted to the charging unit. Various automatic and display functions are provided in the signal-generator unit and in the charging unit.