Electrolysis uses electricity to break water apart, and more batteries mean faster results. More voltage pushes more current through the solution, so the hydrogen gas collects faster each time you add another battery.

Running electricity through salt water splits the water apart, and the hydrogen gas that forms is visible as bubbles collecting on the copper electrodes. Two copper wires sit in a beaker of salt water and connect to batteries. As current flows, hydrogen gas rises into an inverted test tube placed over one wire. More voltage pushes more current through the solution, so the gas collects faster each time you add another battery.