Choosing the right battery for your boat can be very confusing, especially if most of your experience is involving cars. There are also a lot of helpful people that will give you wrong information about batteries, it's not their fault, this is a long-standing problem even among some battery sales people. Let's examine the difference between the regular marine battery, the deep cycle battery for marine use, and the AGM marine type battery now.
Automotive Batteries Will Start Your Engines Fine
The problem with using a car battery in your boat is that they're constructed differently inside. Boats tend to slam into the waves hundreds of times per hour and a car battery isn't made to take the hits.
If you were to open up the two types of batteries you would immediately see that the lead plates are laid out differently in each of them. The marine battery is built to take a constant pounding at wildly different angles as the boat goes vertical one minute and horizontal the next.
You'll also see that there are spacers and supports separating the plates in the marine style battery that helps keep them apart. Once they touch, that part of the cell is shorted out and dead. A car battery won't have the spacers or the extra support because it doesn't need them.
A Deep Cycle Marine Battery Is Different As Well
A deep cycle battery is made to run appliances like refrigerators, radios, and microwaves or run electric trolling motors. These uses draw low amounts of power over long periods of time. If you run a deep cycle battery all the way down, it will still take a charge and not be ruined like a regular battery would.
The difference between the "marine" deep cycle and a regular deep cycle is again, the supports for the plates inside so it can take the beating of being on the water and pounding the waves. Other deep cycle batteries are used in solar applications, golf carts and computer backup UPS devices.
An AGM Battery Is Built To Take Up Side Down Use
AGM stands for "absorption glass mat" and that's because there are mats, similar to fiberglass, built into the battery between the lead plates. These batteries are slightly more powerful that regular batteries and can also handle being completely turned upside down during usage without spilling or harming the battery.
These batteries are especially good when used in applications where the vehicle will be in many different positions, like boats, ATV's, 4 wheel drives, and airplanes. The military is especially fond of then because many military uses involve off-road driving and they need a dependable battery at all times. Regular batteries are prone to leaking and the battery acid is especially bad for electronic components that could be ruined by just one spill.
Now that you can see the differences between the different batteries you can understand why people get so confused. When you go into the battery store it's important to explain the exact uses that the battery will be used for in order to get the right one for your application.