Optima batteries come in several standard group sizes, not a single one. The exact group size depends on the battery line and the application, with common options including Group 34/78 for automotive starting batteries, Group 75/25 for deep-cycle YellowTop models, and marine-friendly sizes like 24M, 27M, and 31M for BlueTop marine batteries.
Understanding Optima's Group-Size System
Optima markets its batteries according to the Battery Council International (BCI) group-size classifications. These define the dimensions, terminal layout, and weight of the battery, ensuring fitment with specific vehicles and equipment. The company maintains a fit-guide and labeling system so consumers and technicians can verify the correct size before purchase. In practice, Optima offers multiple group sizes to cover automotive starting needs, deep-cycle use, and marine applications, rather than a single universal size.
Common Group Sizes Optima Uses
The following group sizes appear most frequently in Optima’s automotive, deep-cycle, and marine lines. They illustrate the range of sizes available rather than a single option.
- Group 34/78 — Automotive starting batteries used in many cars and light trucks; some configurations feature dual terminals for flexible wiring.
- Group 75/25 — Deep-cycle capability used in certain YellowTop models, suitable for higher electrical demand or extended accessory use.
- Group 24M — Marine/ RV-sized group used by BlueTop Marine models, common on mid-sized boats and off-grid setups.
- Group 27M — Larger marine deep-cycle option used on some boats and RVs needing higher capacity.
- Group 31M — Large-capacity marine/RV battery used when maximum reserve capacity is required.
These examples show the breadth of Optima’s offerings, but the exact group size you need depends on your specific vehicle or vessel and the Optima model selected. Always verify the correct group size by checking the battery label, your owner's manual, or Optima's official fit guide.
How to Find the Right Optima Group Size for Your Vehicle
To ensure you pick the correct group size, start with the vehicle or equipment’s original battery specification and the Optima fit finder. You should check the battery’s model number and BCI group size printed on the label, compare to your manual, and confirm terminal configuration and dimensions to ensure a proper fit.
Tips for Verifying Fit
Tip: If you’re replacing an existing Optima, physically compare length, width, height, and terminal arrangement with the new battery. For boats or RVs, consider reserve capacity and amp-hour ratings in addition to group size to avoid power shortfalls.
In case of confusion, contact a retailer or Optima support for confirmation before purchasing.
Summary
Optima batteries cover multiple standard group sizes; there is no single group size for the whole lineup. Common options include 34/78 for automotive starting batteries, 75/25 for certain deep-cycle YellowTop models, and marine-oriented sizes such as 24M, 27M, and 31M. Always verify the correct group size with the vehicle manual, battery label, or Optima’s fit guide to ensure a proper match.
What type of battery is the Optima battery?
AGM
Optima® batteries are ultra high performance AGM products with advanced Spiralcell® Technology that can outperform all other lead-acid batteries.
Is a group 27 battery bigger than a group 24?
Group 27 batteries are typical in size, but larger than Group 24 batteries. The dimensions are 12.5" L x 6.75" W x 9.37" H. These batteries are commonly used in RVs, boats, off-grid systems, and backup power systems.
Are group 24 and 34 batteries the same?
The reserve capacity rating on the Group 34 BLUETOP is 120 minutes, while the Group 24 reserve capacity rating is 140 minutes. The OPTIMA Group 34 battery is an AGM (absorbed glass mat) lead-acid battery, while the Group 24 is a flooded lead-acid battery.
Are group 34 and 78 the same?
However, BCI group sizes can be very confusing, including the Group 34/78 battery size. The "34" number refers to a battery of specific dimensions with top terminals, while a "78" number also refers to a battery of specific dimensions with side terminals.