1. An implantable cardioverter defibrillator (ICD) configured to be communicatively coupled to an external system, the ICD comprising: a defibrillation circuit configured to deliver defibrillation shock pulses each having an amount of energy programmed to a shock pulse energy level, the defibrillation circuit providing for a programmable ICD energy level and including a defibrillation capacitor, the ICD energy level being a maximum energy level up to which the shock pulse energy level is programmable, the defibrillation capacitor configured to store the energy for each of the defibrillation shock pulses; an implant telemetry circuit configured to receive one or more programming parameters controlling the ICD energy level from the external system; and an implant controller coupled to the defibrillation circuit and the implant telemetry circuit, the implant controller including an energy level control module configured to control the ICD energy level by controlling a maximum charging level and a reform charging level using the one or more programming parameters, the maximum charging level being an energy level to which the defibrillation capacitor is charged in preparation for the delivery of each of the defibrillation shock pulses, the reform charge level is an energy level to which the defibrillation capacitor is charged in a reforming process when none of the defibrillation shock pulses is being delivered, wherein the ICD has an energy efficiency that is increased by decreasing a difference between the ICD energy level and the shock pulse energy level.