There are several batteries in most boats that are important and used in different ways. The primary boat batteries are used to start the engine in the craft and can be a single battery or several batteries used in a series. The second type of battery used is for electricity storage to run lights inside the boat, accessories that need to run when the boat is not running. On small boats, you might use it to operate a trolling motor for moving around without the main engine running.
If you need to replace the starting batteries in your boat, you can find the right type at a marine battery supply, and often they are available in several standard sized and power ratings based on the engine size. Most boat batteries for engine starting are twelve-volt units and rated with cold-cranking amps, just like car batteries, and are charged off the engine's generator or alteration once it is running.
The battery's physical size is essential with boats because there is typically a limited amount of space for storing them. In a larger vessel, the boat batteries likely live near the engine, but in small boats, they can be just about any place there is room, making it more critical to get the correct power rating. Because the power cables may have to run some distance from the batteries to the engine, a voltage drop is often a concern and can worsen the longer the cable run is.
Locate your starting batteries as close to the engine as you can do safely. The boat batteries must be secure so they don't move around, and they must fit appropriately in the space provided in the boat.
Deep Cycle Marine Batteries
The second most commonly used boat batteries that you may need to replace are deep cycle marine batteries and are often used in other applications outside the marine environment because of their ability to store power for long periods. These batteries are designed to be fully charged and then discharged slowly to power many different things for several hours or several days.
On larger vessels like boats with closed cabins or pleasure craft designed to go out for a few days at a time, you will often use these boat batteries to power the lighting, the emergency radios, and other small electrical-powered items. When stored in a bank of several batteries, they can be charged at the dock and then used when out on the water, connected to a solar collection grid on the boat, or for small boats, a single deep cycle battery can be charged at home and then brought to the boat for a day on the mater.
Your local marine battery supply can help you select the correct replacement battery for your boat size and use. If the battery you were using worked fine but just got old, you can replace it with the same size and type more often than not.