Calculator
Example data table
| Pack | Avg Power (W) | Mass (kg) | Volume (L) | W/kg | W/L |
|---|---|---|---|---|---|
| 48V 10Ah e-bike pack | 1,800 | 3.2 | 2.4 | 562.5 | 750.0 |
| 14.8V 5Ah drone pack | 900 | 0.62 | 0.45 | 1451.6 | 2000.0 |
| 400V EV module (est.) | 25,000 | 32 | 18 | 781.3 | 1388.9 |
Formula used
Volumetric power density (W/L) = Pavg / V
Pavg = Voltage(V) × I × Efficiency × VoltageFactor × Derating
How to use this calculator
- Choose Direct average power if you already have measured power.
- Or choose Estimate and enter voltage, capacity, and either C-rate or discharge time.
- Add mass for W/kg and volume for W/L outputs.
- Adjust efficiency, voltage factor, and derating to match real conditions.
- Press Calculate. Download CSV or PDF for documentation.
What power density indicates in pack selection
Power density expresses how much power a battery can deliver relative to its mass or volume. It supports tradeoffs when weight and enclosure size matter. A high W/kg figure suits drones, handheld tools, and performance vehicles. A high W/L figure helps when packaging space is fixed, such as racks and mobility frames.
Building the average power estimate
The calculator accepts either measured average power or an estimated electrical model. In estimate mode, average current is derived from capacity and either C-rate or discharge time. It converts electrical power to delivered power using efficiency, an average voltage factor, and a derating margin. Mass and volume are converted to kg and liters. Enter pack voltage as the bus value and capacity as rated amp‑hours at the same discharge rate. For series/parallel assemblies, use total pack voltage and the effective parallel-group capacity. Include casing in mass and volume for accurate densities.
Conditioning factors for realistic results
Efficiency captures losses in conductors, protection devices, and conversion stages. Voltage factor approximates sag between nominal and under-load average voltage. Derating accounts for temperature, state-of-charge limits, aging, and conservative design rules. Together they prevent optimistic results that can mask overheating or early voltage cutoff. For burst operation, the peak factor scales average power to a controlled short-duration target.
Practical benchmark ranges
Typical gravimetric power density varies by chemistry, cell format, and pack layout. High-discharge packs for drones can exceed 1200 W/kg at short duty cycles, while commuter mobility packs often sit between 300 and 800 W/kg for longer runtimes. Volumetric power density in compact enclosures may range from 600 to 2000 W/L depending on cooling, interconnects, and allowable voltage drop. Use measured limits whenever possible.
Documentation and validation workflow
For engineering documentation, export results after each scenario change and label packs clearly. Compare “best case” and “hot day” settings by adjusting derating and voltage factor, then keep both files with the test log. Validate any estimate against datasheets, continuous current ratings, and temperature rise data. If measured power exists, use direct mode as the primary reference.
FAQs
1) What is the difference between power density and energy density?
Power density is how fast energy can be delivered (W/kg or W/L). Energy density is how much total energy is stored (Wh/kg or Wh/L). A pack can have high energy density yet modest power density if discharge current is limited.
2) Why do I see “—” for W/kg or W/L?
The calculator needs mass for W/kg and volume for W/L. If a value is missing, zero, or non-numeric, the related metric is hidden to avoid misleading results. Enter the full pack mass and enclosure volume for accuracy.
3) What should I enter for average voltage factor?
Use 1.00 when voltage stays close to nominal. Use 0.85–0.98 if voltage sags under load due to internal resistance, cold temperature, or high current. If you have test data, use average loaded voltage divided by nominal voltage.
4) When should I use Direct mode instead of Estimate mode?
Use Direct mode when you have measured average power from a load profile, dynamometer test, or logged inverter output. Use Estimate mode early in design when you only know voltage, capacity, and a target discharge rate or time.
5) How do I choose a reasonable peak factor?
Set peak factor to the ratio of expected burst power to average power. For mild transients, 1.1–1.3 is common. For aggressive bursts, use the shortest realistic duration and confirm the pack’s pulse current and temperature limits.
6) Why is derating important in power density calculations?
Derating reduces optimistic power to reflect real constraints such as heat, aging, state-of-charge limits, and safety margins. Using 80–95% is common for continuous duty. It helps prevent designs that meet numbers on paper but fail in field conditions.