Top 3 Marine Battery Group Sizes

At Marine Battery, we get this question a lot:

What does Group Size mean in regards to Marine Batteries?

In the world of marine batteries, the term “group size” refers to the battery’s physical dimensions (length, width, and height), and it’s a critical factor for ensuring the battery fits properly in your boat’s battery tray. While there are many group sizes available, the following three are the most common and versatile for a wide range of marine applications:

1. Group Size 24: This is a popular choice for smaller to medium-sized boats. Group 24 batteries are compact and lightweight, making them suitable for vessels with limited space and modest power demands. They are often used as starting batteries for outboard motors or as a power source for basic electronics like a fish finder and a few lights.
2. Group Size 27: A step up from Group 24, a Group 27 battery is slightly larger and offers a greater amp-hour (Ah) capacity and higher cold-cranking amps (CCA). This makes them a great dual-purpose option for mid-sized boats that need reliable starting power and a decent amount of reserve capacity for running trolling motors, navigation equipment, and other onboard accessories for extended periods.
3. Group Size 31: This is the go-to size for larger boats and those with more significant power needs. Group 31 batteries are the largest of the three, providing the highest capacity and CCA. They are ideal for high-performance applications, such as powering multiple electronics, a refrigerator, a livewell pump, or a trolling motor for long hours. They are a common choice for house batteries in larger vessels or as a powerful starting battery for large engines.