An implantable medical device includes a low-power circuit and a multi-cell power source. The cells of the power source are coupled in a parallel configuration. The implantable medical device includes both a low power circuit and a high power circuit that are coupled between the first and second cells. An isolation circuit is coupled to the first cell and the second cell in a safe parallel orientation and the first and second cells are configured in a first configuration to deliver energy to the low power circuit segment and in a second configuration that is different from the first configuration to deliver energy to the high power circuit segment. A monitoring circuit is coupled to the power source and operable to evaluate the first cell and the second cell to detect a fault condition associated with at least one of the first and second cells.
