How do batteries produce a certain voltage, such as 1.5V or 9 V? From what I understand, battery EMF comes from oxidation of the anode, which releases electrons that can flow through a circuit. But how do batteries regulate that voltage? What is it about the chemical reaction that creates an electric potential difference of a predictable quantity?
The voltage generated by an individual electrochemical cell will be in the approximate range of a fraction of a volt to a volt and a half for most cells and is determined by the particulars of the anode oxidation process, which vary from one metal to another as you point out.
However, to get 6 volts or 9 volts or 12 volts we have to string together individual cells in series, so their cell voltages add up. The result is called a battery; a 12 volt car battery consists of 6 lead/acid cells in series and a 9 volt radio battery contains 6 zinc/carbon cells in series.