AA, AAA, C and D "batteries" are commonly used items that power many of today's electronic gadgets.
AA, AAA, C and D "batteries" are not actually batteries. They are cells. When two or more cells are combined, they form a battery. A battery is actually a group of cells that are working together. A 9v battery is a true battery. Inside a 9v battery are 6 1.5v cells which are sometimes round AAAA batteries.
Merriam-Webster Online defines battery as: "a group of two or more cells connected together to furnish electric current" (definition 4b). 
Contrary Evidence and ArgumentsEdit
Merriam-Webster Online provides an alternative definition for battery (definition 4b, "also"): "a single cell that furnishes electric current."
Pending submission of evidence.