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Today, we are going to cover how to determine the power densities of various batteries. Power density is an important concept when comparing different batteries because it helps us understand how much energy a battery can store relative to its physical size.
Understanding Battery Power Density – VIDEO
Introduction to Power Density
We’ll start by looking at two examples: a 100-amp-hour, 12-volt battery, and a 200-amp-hour, 12-volt battery. Although both are 12 volts, the cells inside are configured differently, which gives each battery a different power density.
For example:
- Battle Born batteries use cylindrical cells, which create small air gaps between cells. This takes up a bit of extra space.
- Victron batteries, on the other hand, use prismatic (rectangular) cells. These cells stack more efficiently, resulting in a higher power density.
Some batteries, like Victron, require an external Battery Management System (BMS), while others have the BMS built in. When calculating power density, we won’t include external components like BMS units.
Methodology
To determine power density, we’ll use the following process:
- Use the nominal voltage of each battery (12V, 24V, or 48V).
- Calculate watt-hours (Wh) using:
Volts × Amp-hours = Watt-hours - Divide the watt-hours by the volume of the battery (in cubic inches).
Watt-hours ÷ Cubic Inches = Watt-hours per Cubic Inch
We’ll round all measurements to the nearest half inch.
Analyzing Battery Examples
Victron Smart Lithium 12V 200Ah
- Capacity: 2,400 Wh
- Dimensions: 12.5 × 6.5 × 9.5 inches
- Power Density: 3.1 Wh/in³
This is a highly power-dense battery.
Battle Born 12V 100Ah
- Capacity: 1,200 Wh
- Dimensions: 12.5 × 7 × 9 inches
- Power Density: 1.52 Wh/in³
Slightly lower power density, which makes sense given the cylindrical cells and compact design.
SOK 12V 314Ah
- Capacity: 3,768 Wh
- Dimensions: 17.5 × 9.5 × 11 inches
- Power Density: 2.06 Wh/in³
Moderate density, with an internal BMS and communication ports that add some bulk.
Epoch 12V 460Ah
- Capacity: 5,520 Wh
- Dimensions: 21 × 8.5 × 11.5 inches
- Power Density: 2.69 Wh/in³
Highly efficient for its size—one of the denser batteries in this list.
Expion 360 12V 240Ah
- Capacity: 2,880 Wh
- Dimensions: 17.5 × 21.5 × 4 inches
- Power Density: 1.91 Wh/in³
Compact and ideal for tight spaces.
Rich Solar 48V 100Ah
- Capacity: 4,800 Wh
- Dimensions: 18 × 18 × 5.5 inches
- Power Density: 2.69 Wh/in³
Same density as the Epoch 460—quite efficient and includes an internal BMS.
Battle Born GC3 12V 270Ah
- Capacity: 3,240 Wh
- Dimensions: 22 × 6 × 13.5 inches
- Power Density: 1.82 Wh/in³
After adjusting for mounting feet, this result places it just above the 100Ah Battle Born.
Ranking and Observations
After calculating the power densities of all the batteries we tested, here’s what we found:
Top 3 Power-Dense Batteries:
- Dakota Lithium 12V 320Ah – Highest power density.
- Victron Energy Smart Lithium 24V 300Ah – A close second.
- Dakota Lithium 12V 640Ah – Impressive capacity and density.
Dakota Lithium batteries showed exceptional power density, although they come at a higher price point. If maximizing capacity in limited space is your priority, they’re a great option.
Power Density vs. Cost
We also compared the price per watt-hour per cubic inch. While this calculation can be interesting, it’s not necessarily practical for decision-making. Because most batteries have similar densities, the least expensive models (like Rich Solar Lite 12V 100Ah) come out ahead in cost-per-density comparisons.
This metric isn’t the best way to select a battery, but it can help visualize the trade-offs between performance and price.
Takeaways
- Prismatic cells generally offer better power density than cylindrical cells.
- Batteries with internal BMS units take up slightly more space but simplify installation.
- Dakota Lithium, Victron, Epoch, and Rich Solar each have their own strengths—choose based on your system needs, space, and budget.
- Always consider not just the battery size but also the space required for wiring and installation.
Conclusion
Today, we explored how to measure and compare battery power densities and learned how different configurations impact storage efficiency.
In the next lesson, we’ll wrap up the Battery Basics series with a discussion on choosing the right battery manufacturer based on your specific needs and experiences from real-world installations.
