24 Group Size

You've seen "Group 24" in your boat manual, your RV spec sheet, or on the old battery you're replacing. Now you need to know what it actually means and what to buy.

This guide explains what the designation actually means, compares the four available chemistries, and covers the specs that matter — so you can pick the right one for your setup.

What is a Group 24 Battery?

Battery group size is a standard set by the Battery Council International (BCI). "Group 24" is one of the most widely used BCI designations — it defines the physical dimensions of the battery case: length, width, height, and terminal placement. It says nothing about what's inside.

Two batteries with the same Group 24 label can be completely different in chemistry, performance, and price. The group number just tells you the battery will fit a specific tray or compartment.

Group 24 Subtypes

Within the Group 24 family, there are several variants that share the same group 24 battery size but differ in height and terminal orientation. Always check group 24 battery dimensions against your compartment before ordering — buying the wrong subtype can cause cable strain, or, in the case of reversed terminals, a polarity short.

Group 24 Battery Types: Which Chemistry is Inside?

Flooded Lead-Acid (FLA)

The oldest and cheapest technology. The electrolyte is in liquid form, so the battery must stay upright and requires periodic water top-ups.

AGM (Absorbent Glass Mat)

The most common Group 24 chemistry. The electrolyte is absorbed into a fiberglass mat, making it sealed, spill-proof, and maintenance-free.

Gel

Similar to AGM in that it's sealed and maintenance-free, but the electrolyte is a silica-based gel rather than a mat. It handles high heat better than AGM but requires a gel-specific charger. Using a standard AGM charger will damage it.

LiFePO4 (Lithium Iron Phosphate)

It's significantly lighter, longer-lasting, and more energy-efficient than any lead-acid chemistry, but comes at a higher upfront price.

Chemistry Comparison at a Glance

Deep Cycle vs. Starting vs. Dual-Purpose

Group 24 batteries come in three functional types, and mixing them up is an expensive mistake.

Starting (Cranking) Batteries

Built with thin lead plates and high surface area to deliver a short, intense burst of current, enough to crank an engine. They are not built for repeated deep discharge. Doing so damages the plates quickly.

Group 24 starting batteries exist but are uncommon. If you need one for a marine engine, look for a dedicated Group 24 marine starting battery and check the CCA rating.

Deep Cycle Batteries

Built with thicker, denser lead plates (or lithium cells) designed to be discharged down to 50–100% of capacity and recharged hundreds or thousands of times. This is where most Group 24 buyers land.

A group 24 deep cycle battery powers trolling motors, RV appliances, and solar storage: anything that runs continuously over hours rather than seconds.

Dual-Purpose Batteries

A compromise between starting and deep cycle. They can crank an engine and handle moderate cycling. They don't do either job as well as a dedicated battery, but on a small boat where you only have one battery compartment, they're a practical solution.

What is a Group 24 Battery Used For?

Group 24 vs. Group 27 vs. Group 31: Which Size do You Need?

Spec	Group 24	Group 27	Group 31
Length	10.25"	12.06"	13.00"
Width	6.81"	6.81"	6.81"
Height	8.88"	8.88"	9.44"
Capacity (AGM)	75–85Ah	85–105Ah	95–125Ah
Reserve Capacity	120–180 min	160–220 min	180–250 min
CCA (typical)	500–840	600–900	800–1,150
Weight (AGM)	43–57 lb	50–65 lb	60–75 lb

Choose Group 24 when your battery tray limits you to this size, or your power demands are moderate: a single trolling motor, basic RV house loads, a small solar system.

Choose Group 27 when you have the space and need more capacity for longer trips, bigger loads, or a larger boat. Group 27 gives you roughly 20–25% more capacity over Group 24 for a modest weight increase.

Choose Group 31 when you need the most capacity in a single battery: large vessels, commercial equipment, or extended off-grid stays.

A group 24 vs. 27 battery swap is worth considering if you're upgrading and have 1.81 extra inches of length available in your compartment. Measure before you order.

Key Specs to Understand Before Buying

Amp-Hours (Ah)

The total energy the battery can store. A 100Ah battery can theoretically supply five amps for 20 hours, or 10 amps for 10 hours. Usable capacity depends on the chemistry and how deeply you can discharge without damage.

Group 24 AGM batteries typically rate at 75–85Ah. Group 24 LiFePO4 batteries commonly offer 100Ah.

Reserve Capacity (RC)

RC measures how many minutes the battery can sustain a 25-amp load before voltage drops below 10.5V. It's a more practical spec than Ah for real-world situations. Think of it as the answer to: how long can this keep my electronics running if my alternator fails?

Group 24 batteries typically range from 120 to 180 minutes of RC. Higher is better.

Cold Cranking Amps (CCA)

CCA is the number of amps a battery can deliver for 30 seconds at 0°F while staying above 7.2V. It only matters if you're using the battery to start an engine in cold weather. For pure deep cycle use (trolling motor, house loads, solar), CCA is largely irrelevant.

Group 24 batteries range from roughly 500 to 840 CCA.

Marine Cranking Amps (MCA)

The same test as CCA, but measured at 32°F instead of 0°F. MCA ratings are always higher than CCA for the same battery. Marine battery listings often show MCA rather than CCA, so keep this in mind when comparing models.

Depth of Discharge (DoD)

DoD is how far down you can drain the battery without damaging it. For AGM and flooded batteries, the safe limit is around 50%. A 100Ah AGM gives you roughly 50 usable amp-hours. LiFePO4 can safely discharge to 80–100%, giving you 80–100 usable amp-hours from the same rated capacity.

A 100Ah LiFePO4 battery effectively delivers nearly twice the usable energy of a 100Ah AGM, which changes the cost-per-usable-watt math considerably.

Cycle Life

One "cycle" is a full discharge and recharge. AGM Group 24 batteries typically deliver 400–600 cycles at 50% DoD. LiFePO4 delivers 3,000–5,000 cycles at full DoD. Factor in replacement frequency, and the long-term cost of lithium often comes out lower.

Weight

Weight matters more than people expect, especially on a boat or in a vehicle. A typical Group 24 AGM weighs 43–57 pounds. A comparable Group 24 LiFePO4 weighs 15–27 pounds. That's a significant difference if you're carrying the battery down a dock or swapping it into a motorized wheelchair.

Terminal Type and Orientation

Always check the terminal layout before ordering. Confusing a standard Group 24 with a 24R (reversed terminals) or a 24F (offset terminal position) is a common and easily avoidable mistake. If your cables barely reach now, a reversed-terminal replacement will create real installation problems.

Group 24 AGM vs. Group 24 LiFePO4: Which is Worth It?

This is the most common buying decision for Group 24 buyers: a group 24 AGM battery or a group 24 LiFePO4 model. The answer depends on your situation.

Match the Chemistry to the Job, Not Just the Compartment

Group 24 is a size standard. It tells you what fits, not what works best. The more useful question is which chemistry fits your use case.

For occasional use on a budget, AGM is the sensible default. It's maintenance-free, widely available, and there's no compatibility headache. For heavy use, solar storage, or situations where weight actually matters, LiFePO4 makes more sense on a per-year cost basis once you account for replacement frequency and the extra usable capacity you get per cycle.

Whichever direction you go, verify the subtype (24 vs. 24F vs. 24R), confirm your charger is compatible, and size the battery to the actual load rather than the compartment.

Browse group 24 AGM and lithium batteries at A1 SolarStore, along with compatible chargers and accessories for marine, RV, and off-grid setups.

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