27 Group Size

"Group 27" is one of those labels that tells you very little on its own. This guide breaks down what the term actually means, the four chemistry types available under it, and how to read the specs — amp-hours, reserve capacity, cold cranking amps — so they map to your actual use. Whether you're powering a trolling motor, an RV, or a solar backup system, you'll leave knowing which Group 27 battery is worth buying and which tradeoffs matter.

What Is a Group 27 Battery?

"Group 27" is a size designation set by the Battery Council International (BCI). It describes the physical dimensions of the case, nothing else. Chemistry, performance, and price all vary; the label just guarantees the battery will fit a Group 27 tray.

Most Group 27 batteries are 12V. Most are built as deep cycle batteries, designed for slow, sustained discharge and repeated recharging. That's a different job from a car battery, which delivers one large burst to start an engine and then stays mostly full.

Group 27 Battery Dimensions and Size

Three sub-variants fall under the Group 27 label. Size differences are small, but a few millimeters can matter if your compartment is tight.

Group 27 battery weight varies considerably by chemistry. Flooded models weigh 50–60 pounds, AGM models 54–70 pounds, and lithium (LiFePO4) models as little as 18–26 pounds. Measure your battery compartment before ordering, including height clearance — that's the dimension people most often overlook.

Group 27 vs. Other Battery Group Sizes

Group 27 sits between Group 24 and Group 31 in both size and capacity. It fits most standard battery trays and doesn't need the larger compartment that Group 31 demands. For most RV and marine buyers, it delivers more runtime than Group 24 without the fitment headache of Group 31.

Types of Group 27 Deep Cycle Battery

"Group 27" tells you the dimensions. Chemistry determines how the battery performs, how long it lasts, and what it costs. There are four options.

Flooded lead-acid (FLA) is the original deep cycle chemistry. The least expensive option, but it needs attention: you'll add distilled water periodically, keep the battery upright, and make sure there's ventilation. For a fixed installation with easy access and a tight budget, it gets the job done.

AGM (Absorbent Glass Mat) is the most widely sold Group 27 battery type. In a Group 27 AGM deep cycle battery, the electrolyte is absorbed into a glass mat, making it sealed, spill-proof, and mountable in almost any position. AGM handles sustained discharge and occasional engine cranking well. It costs more than flooded, but you get maintenance-free operation in return — no water checks, no off-gassing to worry about.

Gel uses a thickened electrolyte. Sealed and maintenance-free, it holds up better than AGM in sustained heat and tends to have a longer cycle life at moderate discharge depths. The catch is that gel is sensitive to high charging currents. The wrong charger can damage it permanently, which is why most buyers end up sticking with AGM.

Lithium (LiFePO4) is a different category. A Group 27 lithium battery weighs about 60% less than a comparable AGM, lasts roughly six to ten times longer in cycle life, and holds a steady voltage until it's nearly depleted. The upfront cost is substantially higher, and older charging systems may need to be upgraded for lithium compatibility.

Deep Cycle vs. Dual-Purpose: What's the Difference?

Group 27 batteries come in three distinct roles. Knowing which one you need saves you from buying the wrong battery.

• Deep cycle batteries have thick plates built for long, slow discharge. Lower CCA, but that's not the point. Use one for trolling motors, RV house loads, and solar storage.
• Dual-purpose batteries balance cranking power and deep cycle capacity. They're the practical choice when one battery has to do both jobs on a boat.
• Starting (cranking) batteries have thin plates optimized for short bursts. They're not built for deep discharge and wear out quickly if used that way.

If your setup runs on a single battery that needs to both start an engine and power electronics, a dual-purpose model is the right call. If you have separate start and house batteries, a dedicated deep cycle on the house side will hold voltage steadier and last longer.

Key Specs When Buying a Group 27 Battery

Amp-hours (Ah) measure total stored energy. Group 27 batteries typically range from 85Ah to 105Ah, though a few outlier models go as low as 66Ah. A 100Ah battery can theoretically deliver 5 amps for 20 hours, though real runtime shortens as draw rate goes up.

Reserve Capacity (RC) tells you how many minutes the battery sustains a 25-amp draw before voltage drops below 10.5V. Group 27 batteries typically land between 140 and 220 minutes. Higher RC means more buffer before you're scrambling to recharge.

CCA and MCA measure engine-starting power. Cold Cranking Amps (CCA) are tested at 0 F; Marine Cranking Amps (MCA) at 32 F, so MCA numbers are always higher for the same battery. For pure deep cycle use, these specs barely matter. For dual-purpose setups, aim for at least 600 CCA or 800 MCA.

Where Group 27 Batteries Are Used

Whether it's a Group 27 RV battery keeping appliances running at a campsite or a marine power source out on the water, this format turns up in a few predictable places:

• Marine and trolling motors: the most common application; as a boat battery, it draws 25–50 amps for hours at a stretch.
• RV house batteries: overnight power for lights, appliances, and climate control.
• Solar and off-grid storage: holds energy from panels for use after dark.
• Onboard electronics: fish finders, GPS, and VHF radios that need stable voltage.
• Backup power: sump pumps, emergency lighting, and UPS systems.

How to Choose the Right Group 27 Battery

Five questions worth settling before you buy:

• Does it need to fit a specific tray? Check whether you need Group 27, 27F, or 27H. Measure the compartment, especially height.
• Does it only run accessories, or also start an engine? Accessories only: deep cycle. Both: dual-purpose.
• How often will you discharge it deeply? Light weekend use: AGM works fine. Daily deep discharge: lithium saves money over the battery's lifetime.
• What's your budget? Flooded for the tightest budgets, AGM for most buyers, lithium when you can spend more upfront for long-term gains.
• Does it start an engine in winter? If yes, check CCA. Aim for 600 or higher in cold climates.

The Bottom Line on Group 27 Batteries

Group 27 covers a lot of ground. It offers more capacity than Group 24, fits where Group 31 won't, and comes in every chemistry from flooded lead-acid to lithium.

For most buyers, AGM is the right chemistry. It's sealed, needs no maintenance, handles vibration without complaint, and lasts long enough to make the price premium over flooded worth it. If you run your battery hard every day — long days on the water, full-time RVing, regular off-grid use — lithium is worth thinking about seriously. The weight savings matter on a boat, and the cycle life math eventually tips in lithium's favor.

When it comes to deep cycle vs. dual-purpose, let your setup decide. One battery doing everything? Dual-purpose. Separate start and house batteries? Pick the right chemistry for each job.

A1 SolarStore stocks Group 27 deep cycle batteries in AGM and lithium, selected for marine, RV, and off-grid applications. Shop by the specs that match your use case, and you'll find a battery that holds up.

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