7. Volta proves the presence of contact tension and produces the battery
In 1796, Volta overcomes all difficulties and turns the tables in his favour. Having invented the condenser electrometer, he used it to show the imbalance of electric fluid by contact between two different metals, without needing the frog.
It is still not entirely clear how, in late 1799, Volta produced the apparatus which was to make him famous: the battery. He made two versions: a crown of cups and a column. Both were based on the pairing of silver and zinc elements separated by moistened conductors. This once more proved that bimetal contact was the real source of electrical power, disregarding any chemical interpretation.

Measuring contact tension, using the condenser electrometer

Cup-shaped and column batteries (from letter to Sir Joseph Banks)