With the proliferation of electronic equipment and gadgets for your boat, batteries are becoming a more important component of modern yachts. In general, marine batteries are 6- or 12-volts and are used to start the engine, as they can produce a large amount of power in short bursts and are recharged with an alternator once the engine is running.
Boats also have deep-cycle batteries, to power the electric equipment of the boat over a long period of time. These batteries are built using a variety of technologies, with the most common being lead-acid batteries, similar to the ones used for automobiles.
State-of-the-art lithium-ion batteries can also be used to handle large capacities and are capable of withstanding many deep-discharge cycles. House batteries typically have fewer (but much thicker) lead plates than starting batteries and are available in capacities of 25AH (amp hours) and 225AH. They are also often wired together to create a bank of batteries with much greater capacities. Look for batteries that meet your anticipated power needs and offer the most charge cycles at 50 percent discharge. Also, be sure that your entire house bank is comprised of a single battery type—never mix battery types (or old and new batteries), as they will have different charge and discharge rates
Some boats usually have dual-purpose batteries, which serve both purposes and are ideal for small boats with space or weight restrictions. However, these batteries are usually not suitable for extended cruises.