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Battery Group Size Chart: Dimensions & Weights (Group 24, 27, 31, U1 & Golf Cart)
Short answer: A battery's group size is a case standard set by Battery Council International (BCI). It defines the outside dimensions of the battery, not its chemistry or capacity. The most common marine and RV sizes are Group 24 (about 10 1/4 in long), Group 27 (about 12 in) and Group 31 (about 13 in), and all three are roughly 6 13/16 in wide. Weight depends on chemistry. A Group 31 battery weighs about 42 to 73 lb in our lineup: about 42 lb for lithium, 54 lb for flooded and 60 to 73 lb for AGM.
Use the chart below to check that a replacement will fit your tray, box or compartment, and to see how much weight a lithium upgrade saves. Every measurement comes from the Pro-Guide battery in that size. Each row links to that battery's full guide.
Key Takeaways
- Group size describes the case only. A Group 31 can be lithium, AGM or flooded, and can be a starting, deep cycle or dual purpose battery.
- Length is what changes between Group 24, 27 and 31. Width stays at about 6 13/16 in.
- Height varies by model, so measure under your hatch or box lid. Pro-Guide's tall Group 31 lithium batteries are 10.83 in tall.
- Lithium cuts weight sharply: the Group 24 100Ah lithium weighs 23.8 lb, compared with 42 lb for the Group 24 AGM.
- Golf cart sizes are named for voltage: GC2 is 6V, GC8 is 8V and GC12 is 12V, and GC2 and GC8 share the same case.
What Is a Battery Group Size?
BCI group numbers let manufacturers build batteries that drop into the same trays, boxes and hold-downs. When a boat builder designs a Group 31 compartment, any Group 31 battery should fit, whatever the brand. A letter or note after the number usually signals a variation. For example, our Group 26G uses bolt-through terminals, and "Group 31 (Tall)" is a Group 31 footprint with extra height to make room for more lithium capacity.
Group size tells you nothing about capacity or cranking power. Two Group 31 batteries can differ by hundreds of cold cranking amps or more than 100 amp-hours. Choose the size to fit your boat, then choose the chemistry and type for the job.
Marine and RV Battery Size Chart (Group 24, 27, 31)
Dimensions are length x width x height in inches.
| Group | Pro-Guide battery | Type | Dimensions (in) | Weight |
| 24 | 12V 100Ah LiFePO4 (24M100) | Lithium deep cycle | 10 1/4 x 6 13/16 x 9 3/16 | 23.8 lb |
| 24 | 12V 100Ah LiFePO4 starting | Lithium starting | 10 1/4 x 6 13/16 x 9 3/16 | 28.7 lb |
| 24 | 480 CCA flooded | Flooded starting | 10 1/4 x 6 13/16 x 8 7/8 | 34 lb |
| 24 | 24M500 flooded | Flooded dual purpose | 10 1/4 x 6 13/16 x 8 7/8 | 36.4 lb |
| 24 | 24M800 flooded | Flooded dual purpose | 10 1/4 x 6 13/16 x 8 7/8 | 42 lb |
| 24 | 24M140 flooded | Flooded deep cycle | 10 1/4 x 6 13/16 x 8 7/8 | 42.4 lb |
| 24 | 935 MCA AGM | AGM starting | 10 1/4 x 6 13/16 x 8 7/8 | 42 lb |
| 24 | AGM deep cycle | AGM deep cycle | 10 1/4 x 6 7/10 x 8 1/5 | 42 lb |
| 27 | 27M160 flooded | Flooded deep cycle | 12 1/16 x 6 13/16 x 8 7/8 | 47 lb |
| 27 | 27M800 flooded | Flooded dual purpose | 12 1/16 x 6 13/16 x 8 7/8 | 49 lb |
| 27 | 27M180 flooded | Flooded deep cycle | 12 1/16 x 6 13/16 x 8 7/8 | 50 lb |
| 27 | 935 MCA AGM | AGM starting | 12 1/16 x 6 13/16 x 8 7/8 | 50 lb |
| 27 | AGM deep cycle | AGM deep cycle | 12 x 6 3/5 x 8 1/5 | 50 lb |
| 31 | 12V 180Ah LiFePO4 | Lithium dual purpose | 13.07 x 6.93 x 8.9 | 41.9 lb |
| 31 | 24V 90Ah LiFePO4 | Lithium deep cycle | 13.07 x 6.93 x 8.9 | 41.9 lb |
| 31 | 36V 60Ah LiFePO4 | Lithium deep cycle | 13.07 x 6.93 x 8.9 | 44.1 lb |
| 31 | 31M225 flooded | Flooded dual purpose | 13 1/16 x 6 13/16 x 9 1/8 | 54 lb |
| 31 | 1150 MCA AGM | AGM starting | 13 x 6 13/16 x 8 7/8 | 60 lb |
| 31 | AGM deep cycle | AGM deep cycle | 13 x 6 4/5 x 8 1/2 | 72.75 lb |
| 31 (Tall) | 12V 235Ah LiFePO4 | Lithium dual purpose | 13.07 x 6.93 x 10.83 | 52.9 lb |
| 31 (Tall) | 16V 160Ah LiFePO4 | Lithium deep cycle | 13.07 x 6.93 x 10.83 | 44.1 lb |
| 31 (Tall) | 24V 115Ah LiFePO4 | Lithium deep cycle | 13.07 x 6.93 x 10.83 | 52.9 lb |
| 31 (Tall) | 36V 75Ah LiFePO4 | Lithium deep cycle | 13.07 x 6.93 x 10.83 | 50.7 lb |
| 31 (Tall) | 48V 60Ah LiFePO4 | Lithium deep cycle | 13.07 x 6.93 x 10.83 | 50.7 lb |
Metric figures and full specs are on each product page and data sheet.
Group size is a footprint standard: a Group 24 lithium battery drops into the same compartment as a Group 24 AGM.
How Much Does a Group 31 Battery Weigh?
In our lineup, a Group 31 battery weighs 41.9 to 72.75 lb, depending on chemistry:
| Chemistry | Group 24 | Group 27 | Group 31 |
| Lithium (LiFePO4) | 23.8 to 28.7 lb | — | 41.9 to 44.1 lb (standard height), 44.1 to 52.9 lb (tall) |
| Flooded lead-acid | 34 to 42.4 lb | 47 to 50 lb | 54 lb |
| AGM | 42 lb | 50 lb | 60 to 72.75 lb |
The comparison that matters most is energy per pound. The 12V 180Ah Group 31 lithium weighs 41.9 lb, nearly 31 lb less than our Group 31 AGM deep cycle, and it is rated at 180 amp-hours. Lithium can also use almost all of its rated capacity, while lead-acid batteries are usually discharged only to about half to protect their life. Read What Is a LiFePO4 Battery? for the full comparison.
Group 24 vs. 27 vs. 31: Which Should You Choose?
- Group 24 (10 1/4 in long): the most compact of the three, common on smaller boats and as a second battery for electronics. It is the lightest option for a given chemistry.
- Group 27 (about 12 in long): adds about 1 13/16 in of length, which in lead-acid means more reserve capacity for trolling motors and house loads.
- Group 31 (about 13 in long): the largest common marine size, used for big outboard starting, high-capacity deep cycle and the highest-capacity lithium options.
Choose the largest size your compartment, tray or box will take, unless weight matters more than capacity. You can usually go down a size, for example a Group 24 lithium in a Group 31 space, as long as you secure it. Going up a size only works if you have the room. The battery box size chart shows which boxes and trays fit each group.
Small Battery Sizes: U1, 26, 26G and 70
| Group | Pro-Guide battery | Dimensions (in) | Weight |
| U1 | 390 CCA LiFePO4 starting | 6.85 x 4.84 x 6.42 | 2.76 lb |
| U1 | 12V 35Ah LiFePO4 | 7 2/3 x 5 1/5 x 6 4/5 | 9.48 lb |
| U1 | 12V 46Ah LiFePO4 | 7 2/3 x 5 1/5 x 6 4/5 | 10.14 lb |
| 26 | 500 CCA flooded starting | 8 3/16 x 6 13/16 x 7 3/4 | 27 lb |
| 26G | 430 CCA flooded starting | 8 3/16 x 6 13/16 x 7 3/4 | 28.2 lb |
| 70 | 550 CCA flooded starting | 8 3/16 x 7 1/16 x 7 5/16 | 28 lb |
Group U1 is the standard lawn mower and garden tractor size, and also a popular kayak and electronics battery. Groups 26 and 70 are compact starting batteries used in gas golf carts and some vehicles. Group 70 has side terminals.
Golf Cart Battery Sizes: GC2, GC8, GC12, J305 and L16
| Group | Voltage | Pro-Guide capacity (20-hr rate) | Dimensions (in) |
| GC2 | 6V | 205, 225 or 235Ah | 10 1/4 x 7 1/8 x 11 1/4 |
| GC8 | 8V | 150 or 165Ah | 10 1/4 x 7 1/8 x 11 1/4 |
| GC12 | 12V | 145Ah | 13 1/8 x 7 1/16 x 11 3/8 |
| J305 / 902 | 6V | 300Ah | 12 7/16 x 7 1/8 x 14 5/8 |
| L16 / 903 | 6V | 370Ah | 12 7/16 x 7 1/8 x 16 3/4 |
| GC2 (lithium) | 48V | 32Ah LiFePO4, 30.42 lb | 10.24 x 7.09 x 10.63 |
GC2 and GC8 share a case, so a cart's battery tray fits either one. What changes is how many batteries you need. A 36V cart uses six 6V batteries, and a 48V cart uses six 8V or four 12V batteries. To skip the battery bank entirely, a single lithium pack replaces the whole set. See our golf cart lithium buyer's guide and conversion guide.
How to Check Fit Before You Buy
- Read the group size on your current battery's label.
- Measure the height from the tray floor to the underside of the lid, hatch or seat. Height is where same-group batteries differ the most.
- Check terminal position and type. Make sure your cables reach the new battery's positive and negative posts, and check whether it has SAE posts, studs or side terminals.
- Confirm the hold-down. Lithium batteries are lighter, but they still need a strap, bracket or box.
Frequently Asked Questions
How much does a Group 31 battery weigh?
In the Pro-Guide lineup, a Group 31 battery weighs 41.9 to 72.75 lb. Lithium models weigh about 42 to 53 lb, the flooded dual purpose weighs 54 lb, and AGM models weigh 60 to 72.75 lb.
What are the dimensions of a Group 31 battery?
About 13 in long and 6 13/16 to 6.93 in wide. Height ranges from 8 1/2 to 9 1/8 in for standard models. Pro-Guide's tall Group 31 lithium batteries are 10.83 in tall.
What is the difference between Group 24, 27 and 31 batteries?
Mainly length. Group 24 is about 10 1/4 in long, Group 27 about 12 in and Group 31 about 13 in, and all three are about 6 13/16 in wide. Larger cases hold more lead-acid capacity, and the extra length adds weight.
Can I put a Group 24 battery in a Group 31 space?
Usually, yes. The smaller battery fits the footprint, but it must be secured so it can't slide. An adjustable box, such as the Group 24-31 Plastic Battery Box, takes up the gap.
How much does a Group 24 battery weigh?
Pro-Guide Group 24 batteries weigh 23.8 to 28.7 lb in lithium, 34 to 42.4 lb flooded and 42 lb AGM.
What does GC2, GC8 and GC12 mean?
They are golf cart battery group sizes. GC2 is a 6V battery and GC8 is an 8V battery, and both use the same 10 1/4 x 7 1/8 x 11 1/4 in case. GC12 is a 12V battery in a longer 13 1/8 in case.
Does group size tell me the battery's capacity?
No. Group size defines the case dimensions only. Capacity, cranking amps and chemistry vary widely within the same group, so check the specs of the specific battery.
Find Your Battery
Know your group size? Start with a lithium battery in that footprint to drop the most weight and gain usable capacity, or browse AGM and flooded options if you're replacing like for like.
Also see AGM batteries, lead-acid batteries and golf cart batteries, or call our team at 1-800-827-3232 and we'll help you match a battery to your compartment.
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