Which of the following starting circuits is NOT used to increase either the voltage or amperage from a set of batteries?

The double series system is not typically used to increase either the voltage or amperage from a set of batteries. Instead, it is a configuration that essentially stacks series connections of batteries to further increase the voltage beyond what a standard series circuit can achieve.

In a series system, batteries are connected end-to-end, which results in a cumulative increase in voltage while the amperage remains constant. When you connect batteries in a parallel system, it maintains the voltage of a single battery while increasing the total available amperage, which can be beneficial for applications requiring more current. The combined system refers to the arrangement that merges both series and parallel configurations, effectively utilizing the advantages of both to enhance voltage and amperage.

In contrast, the double series system focuses solely on voltage enhancement and does not directly address the increase in amperage in the way the other configurations do. This distinction makes the double series system unique and clarifies why it is not categorized in the same manner as the others regarding their function of increasing output metrics.