Improved assemblies, systems, and methods provide an implantable pulse generator for prosthetic or therapeutic stimulation of muscles, nerves, or central nervous system tissue, or any combination. The implantable pulse generator is sized and configured to be implanted subcutaneously in a tissue region. The implantable pulse generator includes an electrically conductive laser welded titanium case. Control circuitry is located within the case, and includes a primary cell or rechargeable power source, a receive coil for receiving an RF magnetic field to recharge the rechargeable power source, and a microcontroller for control of the implantable pulse generator. Improved assemblies, systems, and methods also provide a stimulation system for prosthetic or therapeutic stimulation of muscles, nerves, or central nervous system tissue, or any combination. The stimulation system provides at least one electrically conductive surface, a lead connected to the electrically conductive surface, and an implantable pulse generator electrically connected to the lead.