Disclosed herein is a secondary battery pack including a plurality of cartridges. For example, in accordance with an embodiment of the present invention, a flip flop is disclosed having a dynamic gain skewed to provide metastability resistance. The MCU receives the battery voltage and the estimation current, sets a voltage of the battery in a key-on state as a first voltage, sets a voltage of the battery after a first period as a second voltage, and calculates an internal resistance of the battery using a difference between the first and second voltages and an average value of the estimation current. A user is given information on software blocks that are stored in the programming device andor in an automation device. The plurality of plate-shaped empty space patterns are formed by drilling holes in the substrate and annealing the substrate to form the spaced-apart plate-shaped empty space patterns.