A historic power source where the liquid electrolyte is absorbed into a layer of sand. This design prevents the corrosive acid from spilling out if the cell is tipped or shaken. Telegraph engineers frequently relied on these rugged cells to power testing equipment aboard cable-laying ships navigating rough seas.
Heard on the job
We need a fresh sand battery to run the continuity tests before dropping the next mile of cable.
Insider tip
While completely obsolete in telecommunications, the principle of immobilizing electrolytes lives on in absorbed glass mat batteries.