You're really stretching my memory from engineering school with your question about batteries and capacitors. Batteries are considered huge capacitors, and in power generation and inverters more commonly known as "accumulators". They are used to hold a fixed voltage and prevent voltage spikes. Just like a capacitor, they store a charge, and then release it on demand, or when the voltage changes to negative. When you try to start a motor and connect the positive terminal to the negative terminal (ground), through a starter as resistance, it discharges. When you charge a battery, it stores the positive AC segment above its ambient level (above 12 Volts positive), and then, when below 12 volts positive, diodes prevent the reverse flow of current (discharge back into the generator). The capacitor concept regarding batteries is true not only for big wet cells, but for the little alkaline batteries as well.

Over the weekend, I will try to draw what I have done to the Atiel electrical system. The reason I redid the electrical system, incidentally, is that I have had two different marine surveyors look at the boat on two separate occasions (going back a few decades) and on both occasions they faulted the electrical system. Since those surveys, the standards for boating electrical systems have been tightened up. If I get it done, I will start a new thread so the design of the electrical system can be discussed as a separate issue.