AC vs. DC
There are two ways electrical energy is transferred. Alternating current (AC), which periodically reverses course, is what we use through our wall sockets at home. Direct current (DC), which flows in one continuous direction, is what is stored in batteries.
Every boat’s onboard batteries provide DC energy to a variety of onboard devices like lights and electronics. Though high power appliances like air conditioners often still require AC from shore power, or the constant use of a generator.