Not all batteries are alike. Sure, they can hold a charge, but they perform differently and subsequently have different uses. A marine battery is not used in a car usually and a car battery is not used in a boat.
There can sometimes be some confusion over battery usage because you’ll find that RV owners may uses a golf cart battery or a deep cycle marine battery inside their vehicle. As an RV is not massively different to a car in the sense of being a road vehicle on wheels that can go from A to B successfully, people get confused about why the mix and match approach to batteries, while still not being able to use certain ones in specific situations.
So, let us explain.
Batteries are designed with different purposes in mind. With a car battery, it’s designed to deliver a significant amount of power to get the engine started. After that, the battery is barely used. This is because the engine turns over, burns through gasoline or diesel (unless it’s an electric car) providing the power to make the car go, turn on the headlights, etc.
In this sense, the car battery provides cranking amps and is a cranking battery. Boats also use similar types of batteries that are rated by their cranking amps, and these too are used to get a boat’s engine started. However, they’re not used to run appliances or gadgets on the boat.
The car battery will need to be charged to avoid it going flat. This is why leaving a vehicle unattended for too long can cause the battery to run down even when it’s been unused. A trickle charger that delivers a minimal amount of fresh charge on a semi-regular basis is the answer to this.
Dual-purpose batteries offer the best of both worlds while not excelling in performance or durability for either. This type of battery that really only intended for boating is designed to deliver sufficient cold cranking amps to get a boat’s engine started but also performs double duty as a deep cycle battery capable of producing regular energy in a sustained manner for a number of hours.
Using a dual-purpose battery isn’t needed with a car as the engine supplies the power once it’s been started and doesn’t stall, but with a boat, it can start it and run boat appliances, a trolling motor and other things. The danger is that it gets so drained with the appliances that there’s not enough juice left to start the engine to head back to shore.
Marine or Deep cycle batteries
This type of battery doesn’t deliver sufficient cold cranking amps to get a boat’s engine (or car engine for that matter) started. Its design is to deliver a smooth, consistent amount of reliable power over several hours while out on the water. Period.