Implantable medical devices in embodiments of the invention may include one or more of the following features: (a) a hermetic enclosure, (b) a low-power control circuit located in the enclosure, (c) a high-power output circuit located in the enclosure for delivering an electrical pulse therapy, (d) a power source and circuitry located in the enclosure for powering the low-power control circuit and the high-power output circuit, the power source and circuitry, (e) a first high-rate cell, (f) a second high-rate cell electrically connected in parallel to the low-power control circuit and the high-power output circuit, (g) and at least one resistive load electrically connected between the first high-rate cell and the second high-rate cell, the at least one resistive load having a resistive value to limit, in the event of an internal short in one of the high-rate cells, the rate by which the shorted high-rate cell drains the other high-rate cell.