Battery Energy
E = V × Capacity
Quick answer
This calculator solves E = V × Capacity for Energy. With Voltage 12 V, Capacity 20 Ah, the result is 0.24 kWh. It solves in 3 directions, so you can enter the values you have and get the one you need.
Calculator
Formula
Description
Battery energy in watt-hours represents the total amount of work a battery can deliver and is calculated by multiplying the nominal voltage by the capacity in amp-hours. This metric allows fair comparison between batteries of different voltages and chemistries. For example, a single 18650 lithium-ion cell at 3.7V and 3Ah stores 11.1Wh, while a 9V alkaline battery at 0.5Ah stores only 4.5Wh despite its higher voltage. To convert watt-hours to kilojoules, multiply by 3.6 (since 1Wh = 3600J).
Variables
- E — Energy in watt-hours (Wh)
- V — Nominal battery voltage (V)
- Capacity — Battery capacity in amp-hours (Ah)
Practical Notes
Nominal voltages by chemistry: alkaline 1.5V, NiMH 1.2V, Li-ion 3.7V, LiFePO4 3.2V, lead-acid 2.0V per cell. Energy density (Wh/kg) varies widely: lead-acid 30-40, NiMH 60-80, Li-ion 150-260, lithium polymer 100-200. Aviation regulations limit lithium batteries to 100Wh for carry-on without approval.
Symbols and units
| Symbol | Meaning | Default unit | Accepted units |
|---|---|---|---|
| E | Energy | Wh | µJ, mJ, J, kJ, Wh, kWh |
| V | Voltage | V | pV, nV, µV, mV, V, kV |
| Cap | Capacity | Ah | mAh, Ah |
Step by step
- 1. What you know: Voltage 12 V, Capacity 20 Ah
- 2. The relation: E = V × Capacity
- 3. Substitute: V = 12 V, Cap = 20 Ah
- 4. Result: Energy = 0.24 kWh
Worked examples
Minimum range
Given: Voltage 0.33 V, Capacity 0.2 Ah
Result: Energy = 0.2376 kJ
Low range
Given: Voltage 3.3 V, Capacity 2 Ah
Result: Energy = 6.6 Wh
Typical
Given: Voltage 12 V, Capacity 20 Ah
Result: Energy = 0.24 kWh
High range
Given: Voltage 0.23 kV, Capacity 200 Ah
Result: Energy = 46 kWh
Maximum range
Given: Voltage 2.3 kV, Capacity 2000 Ah
Result: Energy = 4600 kWh
Solving for each variable
Solve for Energy
Voltage 0.33 V, Capacity 0.2 Ah → 0.2376 kJ
Solve for Voltage
Energy 3.6 kJ, Capacity 0.2 Ah → 5 V
Solve for Capacity
Energy 3.6 kJ, Voltage 0.33 V → 3.03 Ah
How Energy changes with Voltage
| Voltage (input) | Energy (result) |
|---|---|
| 1.2 V | 24 Wh |
| 3 V | 60 Wh |
| 6 V | 120 Wh |
| 9 V | 0.18 kWh |
| 12 V | 0.24 kWh |
| 18 V | 0.36 kWh |
| 24 V | 0.48 kWh |
| 48 V | 0.96 kWh |
| 84 V | 1.68 kWh |
| 120 V | 2.4 kWh |
The same result in other units
| Unit | Value |
|---|---|
| J | 864000 |
| kJ | 864 |
| Wh | 240 |
| kWh | 0.24 |
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<p><a href="https://vbatpower.com/formulas/battery-energy/">Battery Energy</a> Calculator by vbatpower.com</p>Frequently asked questions
How do you calculate Battery Energy?
Use E = V × Capacity. With Voltage 12 V, Capacity 20 Ah, Energy works out to 0.24 kWh.
What is the formula for Battery Energy?
The formula is E = V × Capacity. Battery energy in watt-hours represents the total amount of work a battery can deliver and is calculated by multiplying the nominal voltage by the capacity in amp-hours.
How do you find Voltage when you know the other values?
Rearrange for Voltage: with Energy 3.6 kJ, Capacity 0.2 Ah, Voltage is 5 V.
How do you find Capacity when you know the other values?
Rearrange for Capacity: with Energy 3.6 kJ, Voltage 0.33 V, Capacity is 3.03 Ah.
What units does Battery Energy use?
Energy is shown in J, kJ, Wh, kWh. Values are held in SI base units internally, so you can mix prefixes without converting by hand.
Related Concepts
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