Common Battery Sizes Reference
Standard capacities, voltages, and energy ratings for the most common battery sizes. Compare 12V, 24V, and 48V energy across the full range of deep-cycle batteries.
Capacity Reference Table
The table below shows the most common battery capacities in amp-hours (Ah) along with their energy output in watt-hours (Wh) at 12V, 24V, and 48V system voltages. Energy is calculated as Ah × Voltage.
| Capacity | 12V Energy | 24V Energy | 48V Energy | Typical Use |
|---|---|---|---|---|
| 7 Ah | 84 Wh | 168 Wh | 336 Wh | UPS backup, alarm systems |
| 18 Ah | 216 Wh | 432 Wh | 864 Wh | Small electronics, scooters |
| 35 Ah | 420 Wh | 840 Wh | 1,680 Wh | Mobility aids, small fish finders |
| 50 Ah | 600 Wh | 1,200 Wh | 2,400 Wh | Small RV, portable solar, trolling |
| 100 Ah | 1,200 Wh | 2,400 Wh | 4,800 Wh | RV, marine house bank, solar |
| 150 Ah | 1,800 Wh | 3,600 Wh | 7,200 Wh | Large RV, off-grid cabin |
| 200 Ah | 2,400 Wh | 4,800 Wh | 9,600 Wh | Large marine, home solar storage |
| 300 Ah | 3,600 Wh | 7,200 Wh | 14,400 Wh | Whole-home backup, commercial |
| 400 Ah | 4,800 Wh | 9,600 Wh | 19,200 Wh | BESS, industrial, telecom |
Energy = Capacity (Ah) × Voltage. Usable energy depends on depth-of-discharge limits for each chemistry.
Sizes by Application
Different applications have different capacity requirements. Here are the most common battery sizes for each use case, along with why that capacity is chosen.
Small Electronics
7–35 Ah. Used for UPS backup, alarm systems, mobility scooters, and portable devices. These batteries are lightweight and compact, suitable for low-power applications with moderate runtime requirements.
RV / Camper
50–200 Ah. Powers lights, refrigeration, water pumps, and electronics while off-grid. A 100Ah LiFePO4 battery provides roughly 1,200Wh — enough for a weekend of moderate camping without shore power.
Solar Backup
100–400 Ah. Stores solar energy for overnight use or grid outages. Sizing depends on daily consumption, panel output, and desired days of autonomy. A 200Ah 48V bank provides 9.6kWh — typical for small home systems.
Marine
50–300 Ah. House banks power navigation, lighting, refrigeration, and electronics. Deep-cycle marine batteries must handle repeated cycling and vibration. 100–200Ah is the most popular range for recreational boats.
Home Backup
200–400 Ah (48V). Powers critical loads during grid outages — refrigerator, lights, internet, medical devices. A 48V 200Ah bank (9.6kWh) can run essential loads for 1–2 days depending on consumption.
Commercial BESS
300+ Ah. Battery Energy Storage Systems for commercial and utility-scale applications. Typically configured in large 48V racks or containers. 400Ah units are building blocks for multi-MWh installations.
Form Factors and Group Sizes
Batteries come in standard case sizes defined by BCI (Battery Council International). Group size determines the physical dimensions, terminal placement, and approximate capacity range. Choosing the right group size ensures proper fit in your battery compartment.
| Group Size | Dimensions (L × W × H) | Typical Capacity | Common Use |
|---|---|---|---|
| Group 24 | 10.25\" × 6.8\" × 9.9\" | 70–85 Ah | Marine, RV, deep-cycle |
| Group 27 | 12.1\" × 6.8\" × 8.9\" | 90–110 Ah | RV, marine house bank |
| Group 31 | 13\" × 6.8\" × 9.5\" | 100–125 Ah | Commercial trucking, marine |
| Group 4D | 20.8\" × 8.5\" × 9.7\" | 150–210 Ah | Large marine, commercial |
| Group 8D | 20.8\" × 11\" × 10\" | 220–300 Ah | Industrial, telecom, BESS |
Rack-mount batteries (common in LiFePO4 systems) use standard 19-inch rack form factors rather than BCI group sizes. These are measured in rack units (U) and are designed for server-rack or wall-mount installations in solar and home backup systems.
Try It
Use the Battery Sizing Calculator to determine exactly how much capacity you need based on your load, runtime, and system voltage.
Open Battery Sizing CalculatorFrequently Asked Questions
What is the difference between a Group 24 and Group 31 battery?
Group 24 and Group 31 refer to BCI (Battery Council International) standard battery case sizes. Group 24 batteries typically hold 70–85Ah, while Group 31 batteries hold 100–125Ah. The physical dimensions differ: Group 24 is approximately 10.25" x 6.8" x 9.9", and Group 31 is approximately 13" x 6.8" x 9.5". Both are common in marine and RV applications.
How do I choose the right battery size for my solar system?
Start with your daily energy consumption in Wh (multiply Ah × voltage). Then determine how many days of autonomy you need. Divide total Wh by system voltage to get required Ah. For example, a 2kWh daily load with 2 days of autonomy on a 48V system needs approximately 83Ah (2000 × 2 / 48 ≈ 83Ah). Always add a 20–30% buffer for depth-of-discharge limits.
Can I mix different battery capacities in a series or parallel bank?
You should never mix different capacities, chemistries, or ages in a battery bank. In series, the weakest cell limits the entire string. In parallel, the weakest battery draws from the others, causing imbalance and premature failure. Always use identical batteries from the same manufacturer and production batch.
What is the most common deep-cycle battery size?
The 100Ah 12V is the most popular deep-cycle battery size across marine, RV, and solar applications. It balances capacity, weight, and cost effectively. For smaller systems, 50Ah is common. For larger installations, 200Ah and 300Ah batteries or parallel banks of smaller units are used.