Battery Capacity Calculator
Convert between Amp-hours (Ah) and Watt-hours (Wh), determine battery specifications based on voltage and energy requirements
Calculation Results
0 Watt-hours (Wh)
What is Battery Capacity?
Battery capacity measures a battery's energy storage ability, expressed in two ways:
- Amp-hours (Ah): The amount of current a battery can supply for a specific duration
- Watt-hours (Wh): The total energy storage capacity
Relationship: Watt-hours (Wh) = Amp-hours (Ah) × Voltage (V)
Usage Tips
For battery design and applications:
- Use Watt-hours (Wh) when comparing batteries with different voltages
- Higher voltage batteries with the same Ah rating store more energy
- For accurate runtime estimation, use our Runtime Calculator
Important Considerations
Actual usable capacity is affected by multiple factors:
- Discharge current (higher current reduces capacity)
- Ambient temperature (low temperatures decrease capacity)
- Battery age and health condition
- Internal resistance energy losses
Related Calculators
Battery Runtime Calculator
Calculate battery runtime under specific load conditions
Go to Calculator →Battery Series-Parallel Calculator
Calculate voltage and capacity for battery series-parallel configurations
Go to Calculator →Frequently Asked Questions
Converting between Amp-hours (Ah) and Watt-hours (Wh) is necessary for several important reasons:
- Comparing different voltage batteries: Batteries with different voltages but the same Ah rating store different amounts of energy. For example, a 12V 100Ah battery stores twice as much energy as a 6V 100Ah battery.
- Standardized energy specifications: Watt-hours are the international standard for expressing energy capacity, making it easier to compare across platforms.
- Matching power consumption: Many devices specify power consumption in watts (W), so converting to Wh makes it easier to estimate runtime.
- Energy storage system design: Larger energy storage systems are typically measured in kilowatt-hours (kWh), requiring conversion from battery specifications.
Rated capacity is measured under ideal conditions, while actual usable capacity is typically lower due to several factors:
- Discharge rate: Higher discharge currents reduce available capacity due to the Peukert effect.
- Temperature: Low temperatures significantly reduce battery performance, especially for lithium batteries.
- Depth of discharge limitations: To extend battery life, batteries are not typically discharged completely.
- Battery aging: Capacity gradually decreases with charge-discharge cycles.
- Self-discharge: Batteries lose charge over time even when not in use.
In practical applications, it's common to add a 30-50% capacity margin to account for these factors.
Energy density is the amount of energy stored per unit weight or volume, a critical factor when comparing battery technologies:
| Battery Chemistry | Gravimetric Energy Density (Wh/kg) | Volumetric Energy Density (Wh/L) | Typical Applications |
|---|---|---|---|
| Lithium-ion (NMC/NCA) | 150-260 | 250-670 | Consumer electronics, electric vehicles |
| Lithium Iron Phosphate (LiFePO4) | 90-120 | 130-200 | Stationary storage, safety-critical applications |
| Lead-Acid | 30-50 | 60-110 | Automotive starting, UPS systems |
| Nickel-Metal Hydride (NiMH) | 60-120 | 140-300 | Hybrid vehicles, lower self-discharge applications |
Higher energy density batteries are ideal for weight and space-constrained applications, while lower energy density batteries may offer advantages in cost, safety, or cycle life.