There is an explanation of how a battery works that says that inside the battery (in the positive charge convention) there is a field and the battery does work on the positive charge against the field to move it from the negative terminal to the positive terminal and it becomes full of potential energy, ready to be used in a circuit.
But from what I understand from a battery (an excess of electrons on one side and a lack of electrons on the other side) there isn't a field inside the battery and the battery doesn't take a charge and move it from one side to the other so it gains potential energy.
What I need is a chemical detailed explanation of how a battery works that tells more about how the battery's electric field is created.
Batteries work by chemical reactions. The current inside a battery is an ion current. And the main point to realize is that the ion current is driven be a concentration gradient, and that it is in a direction opposite to the electric field inside the battery.