In an electrical diagram with two identical compatible 12 V nominal batteries suitable for series connection, which link gives 24 V nominal between the two free terminals?

Correct answer

The positive terminal of one with the negative terminal of the other.

Link one battery’s positive terminal to the other’s negative terminal: this is a series connection, with output taken between the two remaining free terminals. Nominal voltages add, 12 V + 12 V = 24 V. For identical batteries, series connection does not double ampere-hour capacity. In parallel, positives are joined together and negatives together: nominal voltage remains 12 V and capacity increases. Real installation must follow the design and manufacturer instructions; this is not a jump-start procedure for a 12 V system.