What is the voltage measurement when two 12V batteries are connected in parallel with a test lead on the negative terminal of one battery and the positive terminal of the other?

When two 12V batteries are connected in parallel, their voltage remains the same as that of a single battery, which is 12 volts. This arrangement allows the batteries to share the load while maintaining a constant voltage.

In this scenario, if a meter is measuring the voltage with a lead on the negative terminal of one battery and the positive terminal of the other, it effectively creates a measurement that spans across both batteries. However, since both batteries are outputting the same voltage, the measurement taken will reflect that constant voltage of 12 volts and not the sum of the voltages, which would occur if they were in series.

This is fundamental to understanding how battery configurations work. When batteries are connected in parallel, the positive terminals connect to one another and the negative terminals do the same, thus the output voltage is equal to the voltage of one battery while the capacity (amp-hour rating) increases.