Battery
AA, AAA, C, and D cells, including alkaline batteries, are of standard sizes and shapes, and have about 1.5 volts. The voltage of a cell depends on the chemicals used.  The electric charge it can supply depends on how large the cell is, as well as what chemicals.  The charge a battery delivers is usually measured in ampere-hours.  Since the voltage stays the same, more charge means a bigger cell can supply more amps, or run for a longer time.