Energy supplied by a source divided by the @E01923@ transported through the source. For a galvanic cell it is equal to the @E01935@ difference for zero current through the cell.
Green Book, 2nd ed., p. 58 [Terms] [Book]
PAC, 1996, 68, 957. (Glossary of terms in quantities and units in Clinical Chemistry (IUPAC-IFCC Recommendations 1996)) on page 971 [Terms] [Paper]