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 being a maximum energy level up to which the shock pulse energy level is programmable; an implant telemetry circuit configured to receive one or more programming parameters related to 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 using the one or more programming parameters, 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.