What type of reaction is used to generate an electrical current in a battery?
While there are many different reactions used in batteries, all the reactions have one thing in common. They are spontaneous oxidation-reduction processes.
The anode of the cell may or may not be an active reagent in the process. It may also simply serve as a surface on which the oxidation of a chemical in the electrolyte takes place. The same is true for the cathode, where the reduction half-reaction occurs.
The electrolyte itself can be acid (as in a car battery), a base (as in all alkaline batteries, or a salt.
Electrons released by oxidation at the anode will travel through an external circuit until they return to the cathode, where the reduction process consumes them. So, the transfer of electrons between reducing agent and oxidizing agent is done by providing an external path - the circuit we wish to power.
A battery is rechargeable if we are able, by applying an external DC voltage slightly greater than the reaction potential of the battery, to cause the reaction to run in reverse.