A spinal cord stimulation (SCS) system provides multiple stimulation channels, each capable of producing up to 10 mA of current into a 1 K&OHgr; load. The SCS system further includes a replenishable power source, e.g., a rechargeable battery, that requires only an occasional recharge, and offers a life of at least 10 years at typical settings. Each of the multiple stimulus channels of the system may be combined with other channels to deliver more than 10 mA of current. Additionally, the SCS system has the capability to stimulate simultaneously on all available channels. Each channel has at least two outputs (one positive and one negative) that can be mapped via a low impedance switching matrix to any electrode contact or the system case, thereby allowing a clinician to provide unique electrical stimulation fields for each current channel. Moreover, this feature, combined with multi-contact electrodes arranged in two or three dimensional arrays, allows “virtual electrodes” to be realized. When the system's replenishable power source is fully charged, the user may operate the SCS system independent of external controllers or power sources. The replenishable power source may be replenished using non-invasive means. The SCS system monitors the state of charge of the internal power source and controls the charging process by monitoring the amount of energy used by the SCS system, and hence the state of charge of the power source. A suitable bidirectional telemetry link allows the SCS system to inform the patient or clinician regarding the status of the system, including the state of charge, and makes requests to initiate an external charge process. Processing circuitry within the implanted portions of the system automatically controls the applied stimulation pulses as a new burst of pulses begins in order to gradually ramp up the amplitude of the pulses to a desired level. Other processing circuitry allows electrode impedance measurements to be regularly made.