EV Battery Capacity: Gross vs Usable
Battery capacity is one of the most quoted yet misunderstood EV specifications. Manufacturers may list either the total (gross) or the usable capacity of the pack, and sometimes the value is not specified at all. Understanding the difference is critical when comparing range, charging speed, and energy efficiency across models.
What Battery Capacity Represents
Battery capacity is the total amount of electrical energy stored in the pack, measured in kilowatt-hours (kWh). It determines how far an EV can travel and how long it takes to charge. However, not all stored energy is available for driving — some is deliberately withheld to protect the battery from premature aging.
Gross vs Usable Capacity
| Type | Definition | Typical Use | Notes |
|---|---|---|---|
| Gross Capacity | The full physical energy content of the battery pack, from 0 % to 100 % SoC. | Used by some manufacturers for marketing or type-approval certification. | Higher figure, but not fully accessible during normal operation. |
| Usable Capacity | The portion of gross capacity made available to the user for driving and charging, typically 90–95 % of total. | Used in engineering data and real-world efficiency calculations. | More accurate reflection of true driving energy. |
Why Usable Capacity Is Lower
To prevent damage and extend battery life, EV manufacturers include buffer zones at the top and bottom of the state-of-charge (SoC) range.
- Upper buffer (near 100 %): prevents overcharging and high-voltage stress that degrade the cathode.
- Lower buffer (near 0 %): avoids deep discharge and copper dissolution at low voltages.
- Thermal buffer: some energy is reserved for pack heating/cooling systems and diagnostics.
As a result, a pack with 82 kWh gross capacity might expose only 77–78 kWh usable for driving.
Typical Ratios and Examples
| Vehicle | Gross Capacity (kWh) | Usable Capacity (kWh) | Usable % of Total |
|---|---|---|---|
| Tesla Model Y Long Range | 82 | 78 | 95 % |
| Volkswagen ID.4 | 82 | 77 | 94 % |
| Hyundai Ioniq 5 | 77.4 | 74 | 96 % |
| BYD Seal | 82.5 | 79 | 96 % |
When the Value Is Not Specified
Many OEM websites and regional spec aggregators list a single figure (for example, “Battery: 35 kWh”) without clarifying whether it refers to gross or usable capacity. When the value is ambiguous:
- Assume it is gross if it appears on a manufacturer’s marketing page or type-approval certificate.
- Assume it is usable if it comes from independent testing or measured telemetry data.
Why It Matters
- Range calculations: depend directly on usable capacity × average efficiency (kWh/100 km).
- Charging time: often quoted relative to usable capacity only; charging the hidden buffers is disallowed by software.
- Battery health monitoring: long-term degradation is tracked relative to the usable portion.
Confusing gross and usable capacity can lead to errors of 5–10 % in range or charging projections.
Real-World Variability
- Software updates can slightly expand or reduce usable capacity to improve longevity or recalibrate displays.
- Cold temperatures temporarily reduce usable capacity due to slower electrochemical kinetics.
- Battery degradation over time effectively reduces usable capacity while gross remains constant.
