Battery Energy Calculator
Calculate battery energy in Wh, mWh, or kWh from nominal voltage and capacity, or solve the same relationship backward to estimate required capacity or nominal battery voltage.
Battery energy is usually the better comparison value when battery packs use different voltages. Capacity in Ah or mAh tells you charge storage, while Wh tells you voltage-adjusted stored energy.
Engineering tool
Battery Energy Calculator
Calculate battery energy, required capacity, or nominal voltage from Wh, Ah, mAh, and voltage.
Use the nominal voltage for energy estimates unless your design requires a specific charge or cutoff voltage.
Capacity is internally converted to Ah. For example, 3000 mAh equals 3 Ah.
Battery Energy
11.1 Wh
Use Wh for energy comparison and Ah or mAh for charge capacity.
Result console
- Battery energy
- 11.1Wh
- Energy
- 11,100mWh
- Energy
- 11.1Wh
- Energy
- 0.0111kWh
- Battery capacity
- 3Ah
- Capacity
- 3,000mAh
- Capacity
- 3Ah
- Battery voltage
- 3.7V
- Voltage
- 3.7V
- Formula used
- EWh = V × CAh
Unit reminder
V × Ah = Wh, while V × mAh = mWh. A 3.7 V, 3000 mAh cell is 11.1 Wh, not 11,100 Wh.
This calculator estimates nominal battery energy from voltage and capacity. Real usable energy depends on discharge curve, cutoff voltage, temperature, aging, load current, internal resistance, protection circuits, and conversion efficiency.
Formula reference
Battery Energy Formulas
The calculator uses watt-hours as the internal energy unit, amp-hours as the internal capacity unit, and volts as the internal voltage unit.
EWh = V × CAhCAh = EWh / VV = EWh / CAhEWh = V × CmAh / 1000EmWh = V × CmAhVariable definitions
- EWh
- Battery energy in watt-hours
- EmWh
- Battery energy in milliwatt-hours
- V
- Nominal battery voltage
- CAh
- Battery capacity in amp-hours
- CmAh
- Battery capacity in milliamp-hours
- Nominal voltage
- Average rated battery voltage used for energy estimates
- Battery capacity
- Stored electric charge, commonly shown as Ah or mAh
- Battery energy
- Stored electrical energy, commonly shown as Wh
Variable Description
- Voltage
- Nominal battery voltage used to convert charge capacity into stored energy.
- Capacity
- Charge capacity in Ah, mAh, or µAh. Capacity alone does not describe stored energy without voltage.
- Energy
- Stored electrical energy in Wh, mWh, or kWh.
- Nominal Voltage
- The representative average battery voltage used for pack energy and datasheet comparisons.
- Watt-Hour
- A practical energy unit equal to one watt delivered for one hour.
- Milliamp-Hour
- A common battery charge-capacity unit. Convert mAh to Ah before calculating Wh.
Worked Examples
Single Lithium-Ion Cell
V = 3.7 V, capacity = 3000 mAh
Energy = 3.7 V × 3 Ah = 11.1 Wh = 11,100 mWh = 0.0111 kWh
12 V Battery Pack
V = 12 V, capacity = 7 Ah
Energy = 12 V × 7 Ah = 84 Wh
Required Capacity
Energy = 60 Wh, voltage = 12 V
Capacity = 60 Wh / 12 V = 5 Ah = 5000 mAh
Nominal Voltage
Energy = 74 Wh, capacity = 20 Ah
Voltage = 74 Wh / 20 Ah = 3.7 V
Power Bank Cell Energy
V = 3.7 V, capacity = 10,000 mAh
Energy = 3.7 V × 10 Ah = 37 Wh before boost conversion losses
Small Coin-Cell Budget
V = 3 V, capacity = 220 mAh
Energy = 3 V × 0.22 Ah = 0.66 Wh = 660 mWh
Engineering Notes
What Is Battery Energy?
Battery energy represents voltage-adjusted stored energy and is commonly used for pack comparison, transport limits, and power budgeting.
Battery Capacity vs Energy
Capacity describes charge storage. Energy describes how much work the battery can ideally deliver at its nominal voltage.
Ah vs Wh
Ah values are only directly comparable when battery voltage is the same. Wh values compare energy across different voltages.
Why Voltage Is Required
A 3000 mAh cell at 3.7 V stores far less energy than a 3000 mAh pack at 12 V.
Nominal Voltage
Nominal voltage is normally used for datasheet energy estimates because battery voltage changes during discharge.
Maximum Charge Voltage
Fully charged voltage is useful for safety limits but can overstate average stored energy.
Cutoff Voltage
The usable end of discharge depends on chemistry, protection limits, and product requirements.
Lithium-Ion Nominal Voltage
Many lithium-ion cells use 3.6 V or 3.7 V nominal ratings, with higher full-charge voltage.
Lead-Acid Battery Voltage
Lead-acid packs are often named by nominal voltage such as 6 V, 12 V, 24 V, or 48 V.
NiMH Battery Voltage
A NiMH cell is commonly rated around 1.2 V nominal, so cell count matters in energy estimates.
Energy in Battery Packs
Series cells increase voltage, parallel cells increase capacity, and both affect total pack energy.
Series/Parallel Packs
For ideal matched cells, total pack energy can be estimated from total pack voltage and total pack Ah.
DC-DC Conversion Losses
A regulator or boost converter reduces usable output energy because efficiency is below 100%.
Power Bank Capacity Ratings
Power banks often advertise internal cell mAh. USB output Wh is lower after conversion losses.
Battery Aging
Usable energy decreases with cycle count, calendar age, storage conditions, and temperature exposure.
Temperature Effects
Cold temperature can reduce available capacity and voltage performance; heat accelerates aging.
Discharge Rate Effects
High load current can reduce usable capacity because of internal resistance, voltage sag, and heating.
Common Mistakes
Treating mAh as Wh
Check whether the design question involves charge, current, power, or energy before selecting units or comparing battery packs.
Using maximum charge voltage instead of nominal voltage
Check whether the design question involves charge, current, power, or energy before selecting units or comparing battery packs.
Comparing packs by mAh without checking voltage
Check whether the design question involves charge, current, power, or energy before selecting units or comparing battery packs.
Ignoring converter efficiency
Check whether the design question involves charge, current, power, or energy before selecting units or comparing battery packs.
Assuming all rated energy is usable
Check whether the design question involves charge, current, power, or energy before selecting units or comparing battery packs.
Using cell ratings for a complete pack without checking series and parallel configuration
Check whether the design question involves charge, current, power, or energy before selecting units or comparing battery packs.
Ignoring cutoff voltage, temperature, and battery age
Check whether the design question involves charge, current, power, or energy before selecting units or comparing battery packs.
Confusing W, Wh, A, Ah, mA, and mAh
Check whether the design question involves charge, current, power, or energy before selecting units or comparing battery packs.
Support reference
FAQ
How do I calculate battery energy in Wh?
Multiply nominal battery voltage by capacity in amp-hours. The basic formula is Wh = V × Ah.
How do I convert mAh to Wh?
Divide mAh by 1000 to get Ah, then multiply by battery voltage. For example, 3000 mAh at 3.7 V is 3 Ah × 3.7 V = 11.1 Wh.
Why is voltage required for Wh conversion?
Ah and mAh describe charge capacity. Energy also depends on voltage, so two batteries with the same mAh rating can store different Wh values.
What is the difference between Ah and Wh?
Ah is electric charge capacity, while Wh is energy. Wh is usually better for comparing battery packs with different voltages.
Does higher mAh always mean more battery energy?
No. A higher mAh rating only means more charge capacity. Battery energy also depends on nominal voltage.
Should I use nominal voltage or maximum charge voltage?
Use nominal voltage for most energy estimates. Maximum charge voltage can overstate usable energy because a battery does not remain at full-charge voltage during discharge.
How many Wh are in a 10000 mAh power bank cell?
At a typical 3.7 V lithium-ion cell voltage, 10000 mAh equals 10 Ah and stores about 37 Wh before conversion losses.
Why is usable output energy lower than cell energy?
Protection circuits, voltage conversion, internal resistance, cutoff voltage, temperature, and aging reduce the energy available at the output.
Related Engineering Guides
Planned Engineering Guide
Battery Capacity vs Energy
Planned Engineering Guide
How to Convert Ah to Wh
Planned Engineering Guide
Understanding Battery Nominal Voltage
Planned Engineering Guide
Battery Pack Energy Explained
Planned Engineering Guide
How Power Bank Capacity Is Rated
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Engineering Disclaimer
This calculator estimates nominal battery energy from ideal unit relationships. Verify real usable energy against the cell or pack datasheet, load profile, cutoff voltage, temperature range, aging, safety limits, and conversion efficiency.