Marine batteries and car batteries share some common features but have major differences in design and discharge. This means that if you need a marine battery, you’ll get far better results by purchasing a specific marine battery than by using a battery designed for a car.
In this guide, we’ll explain the key differences between batteries designed for use with a boat, and batteries designed for use in a car. We’ll also explain why you should never even consider using an automotive battery to power your boat’s inboard or outboard motor.
Cranking batteries vs. Dual purpose batteries
Marine and car batteries have several major differences. The first, and biggest, is the purpose of each battery.
Car batteries are designed to do one thing: start a car’s engine. Once the car is switched on and the engine is running, the battery does very little. The engine powers the car’s electrical systems and, at the same time, recharges the battery to make up for the power used to start the car.
In simple terms, a car battery is a “starting battery” or “cranking battery.” Its job is to provide the necessary power to start the car’s engine. Once that’s done, it’s job is over.
Marine batteries, on the other hand, are designed to both starts an engine and provide energy for other devices aboard the boat. This means that a marine battery needs to provide the short jolt of energy required to start an engine and provide a gradual supply of energy for appliances.
If the battery delivered an engine-starting jolt of energy to an onboard hi-fi system or television, it wouldn’t be of much value. In fact, there’s a serious risk that it could damage the appliances on board the boat.
This means that a marine battery needs to be able to crank an engine (like a cranking or starting battery) and provide energy in a deep cycle that draws a smaller amount of energy over a longer period.
In short, it needs to do two things at once. This is why most marine batteries are “dual purpose” batteries — since they can deliver both a large amount of energy to crank an engine and start it up and deliver a consistent supply of energy for electrical devices and appliances.
To illustrate these differences, battery manufacturers use units like “cold cranking amps” (CCA) to show the maximum discharge current of an automotive or marine battery. Batteries with lots of cold cranking amps are more powerful, and more likely to be able to start a large engine.
Dual purpose batteries, which are more common in the marine battery world, are rated both for cold cranking amps and in units like amp hours (Ah), which measure the amount of current that discharges from the battery over 20 hours to bring it to 10.5 volts at a temperature of 80°F.
Another common unit used exclusively for marine batteries is “marine cranking amps,” which measures a battery’s maximum discharge at a temperature of 32°F.
Marine battery and car battery design differences
Marine batteries and car batteries not only deliver power in different ways — they’re also made to different standards. Since car batteries don’t need to discharge energy after starting the car’s engine, they typically have thin internal plates.
For a marine battery, which needs to provide constant energy for the boat’s electronic systems, the internal plates tend to be thicker. The housing of the battery, usually made from plastic, also has a thicker design to better insulate the battery against vibration and impact.
Since boats typically go on rougher journeys than cars (the ocean is, after all, far bumpier than the highway) this thicker plastic housing allows the battery to have a longer functional lifespan, preventing it from needing to be frequently replaced.
Always use a marine battery for your boat
Purchasing a car battery can seem like a great way to save money — after all, car batteries tend to be much cheaper than marine batteries. However, there’s a serious chance that you’ll end up spending more than you expected to when the battery doesn’t work as you expected it to.
Marine batteries are designed specifically to meet the needs of a modern boat. They’re stronger, heavier and more suited to the unique needs of a boat with an inboard or outboard motor. Take good care of them, and they’ll last for several years of continuous use.
In closing, there’s no “do-everything battery.” As tempting as it might be to “save money” with a car battery, the only option you should ever consider for your boat is a dedicated marine battery.