Cell

A 12 V battery is not a 12 Volt cell. A single cell is just what it says, with few exceptions a battery is a group of cells wired in series or parallel to provide the required output in volts or current.

For example a simple D size torch battery is comprised of 3 elements. A carbon rod that is the +(positive) contact an electrolyte paste and then a zinc rich outer shell that is the negative electrode. By themselves they will produce 1.56v because of there chemical reaction These are a single cell. Put them in your torch or radio and they are normally in series 1.56+1.56+1.56= 4.68v.
This is now a battery and no longer a cell

A standard cell :

A standard cell: Is a cell made from a chemically pure material, normally Mercury and some of its oxides, When combined these materials yield up a standard and reliable voltage of 1.023v this type of cell has been used for many years to calibrate sensitive instruments.