What Is a Group 27 Battery? | Size, Specs And Buying Basics

A Group 27 battery is a standardized 12-volt battery measuring about 12 inches long, used mainly in marine and RV applications with 85–110 Ah capacity.

A Group 27 battery is a standardized 12-volt size defined by the Battery Council International (BCI) for mid-size marine and RV applications. Understanding what a Group 27 battery is—its dimensions, capacity ratings, and chemistry options—helps you choose the right power source for your boat, camper, or off-grid setup. This size strikes a balance between runtime and physical footprint, making it a go-to for owners of mid-size boats and travel trailers.

Group 27 Battery Dimensions And Specs

The BCI Group 27 size measures roughly 12.06 inches long, 6.81 inches wide, and 8.88 to 8.94 inches tall. These dimensions can shift slightly depending on the chemistry—AGM and lithium models sometimes differ in height from flooded lead-acid versions, and lithium batteries often pack the same footprint into a much lighter package.

Group 27 is roughly 2 inches longer than Group 24 and about 1 inch shorter than Group 31, so measuring your battery tray is the first step to confirm fit. Terminal placement also varies by manufacturer—check post configuration before buying. These batteries handle starting mid-size outboard engines from 75 to 250 horsepower, serve as deep-cycle house banks for RVs, and work in backup power setups. Reserve capacity of 140–200 minutes means a Group 27 can run accessories for hours before needing a recharge.

What Types Of Group 27 Batteries Are Available?

Three main chemistries dominate the Group 27 market, each with distinct trade-offs in cost, weight, and maintenance requirements.

Flooded lead-acid batteries are the traditional workhorse. They cost $120–$160, deliver 85–110 Ah, and require ventilation because charging releases hydrogen gas. You will need to check water levels periodically and keep the battery upright to prevent spills. They remain the most affordable option for boaters and RVers on a budget.

AGM (Absorbent Glass Mat) batteries are sealed and maintenance-free. Priced at $180–$280, they handle vibration better than flooded types and perform well in marine environments where motion and moisture are constant. AGM is the most common upgrade for boat owners who want reliable starting power without the upkeep. They also work well in RVs where the battery may be mounted on its side.

Lithium (LiFePO4) batteries are the premium option at $350–$600+. A lithium Group 27 weighs just 18–25 pounds—roughly a third of the weight of a flooded battery—and delivers more usable capacity throughout its discharge cycle. Lithium charges faster and lasts 10 years or more. For a side-by-side comparison of the top lithium models, see our top Group 27 lithium battery recommendations.

GEL batteries are available in Group 27 but less common than AGM. They offer deep-cycle durability with slower charge acceptance and suit stationary solar or backup power setups where ventilation is limited. GEL batteries require a charger tuned to their voltage profile, so they are not a drop-in replacement for flooded or AGM in most marine applications.

How Much Does A Group 27 Battery Cost?

Pricing follows the chemistry ladder. Flooded lead-acid models run $120–$160 and offer the lowest upfront cost. AGM batteries land between $180 and $280, with the premium reflecting their sealed, maintenance-free design. Lithium versions range from $350 to over $600, with higher initial cost balanced by a lifespan of 10–15 years and significant weight savings.

Common Group 27 models include Optima’s 8027 (BlueTop, dual-purpose) and 8127 (RedTop, starting-only), US Battery’s UUS-27, and Weize’s Group 27 AGM and lithium offerings. MK Battery makes AGM and GEL versions under the 8A27 and 8G27 part numbers. Flooded options like Remy’s DC27 remain widely available for budget-conscious buyers. Prices reflect 2024–2025 market data and vary by retailer.

Match the battery type to your use case. Starting batteries need higher CCA for brief high-draw bursts. Deep-cycle batteries prioritize Ah capacity for sustained discharge. Dual-purpose models like the Optima BlueTop balance both, making them popular for boats that need starting power and trolling motor runtime from a single battery.

FAQs

Can I use a Group 27 battery in my car?

A Group 27 battery can fit some cars with large battery trays, but it is about 2 inches longer than a standard Group 24 car battery. Measure your tray space and check terminal orientation before purchasing. Most passenger cars use Group 24 or Group 34, so Group 27 is more common in trucks, SUVs, and larger vehicles.

What is the difference between Group 24 and Group 27 batteries?

Group 27 batteries are roughly 2 inches longer than Group 24, with higher amp-hour capacity—85–110 Ah versus 70–85 Ah. The extra capacity makes Group 27 the preferred size for marine deep-cycle use where longer runtime between charges matters. Weight also increases by 10–15 pounds going from Group 24 to Group 27.

How long does a Group 27 battery last?

Lifespan depends on chemistry and usage patterns. Flooded lead-acid Group 27 batteries typically last 3–5 years with regular maintenance. AGM models last 4–7 years. Lithium (LiFePO4) batteries can last 10–15 years depending on charge cycles and depth of discharge. Using a charger matched to the battery chemistry significantly extends service life.