The Columbia 26 we sailed last year seems so quaint now. It had no running water or head (toilette to the rest of you). It had no AC shore power and it's DC power consisted of a single battery charged by an outboard motor and a solar panel. It ran the running lights and VHF radio when necessary.
Speakeasy is a bit more complicated and I've been slowly getting the hang of it. There are two massive batteries (4D in the business), a DC control panel, and an AC control panel. I discovered this week that one of the batteries would not hold a charge. I madly read everything I could about marine batteries. I learned about house and starter batteries and of matched pairs of batteries. I learned about alternators, regulators and panel switches. I learned that marine batteries are expensive. I bought two this morning. My back is telling me how heavy they are, too.
One way to charge batteries is with the engine, which runs an alternator for the purpose. It takes a long time for a small alternator to charge a flooded (wet) lead-acid battery--hours. An alternative method is to plug the boat into shore power--a power plug on the dock--but it still takes hours to charge. To replenish our good battery and see if more charging might help the bad one, we motored to the dock last evening and plugged in. There was no power! This power struggle is getting to me. However, more experienced sailors tell me that I missed a circuit breaker so I'm off to try the shore power again. Wish me luck!