Ah
Capacity
mAh and Ah describe the amount of electrical charge a battery can provide under defined test conditions.
ZERNE Battery Calculation Tool
Lithium Battery Capacity and Energy Calculator
Calculate nominal battery energy from capacity and voltage, convert mAh to Wh, or work backward from energy to estimated capacity. Use the tool for lithium-ion batteries, lithium polymer batteries, LiPo cells, 18650 cells, and battery packs.
mAh, Ah, Wh, and kWh conversionNominal voltage basedSingle-cell and pack planning
Whenergy planning
ϟ
Ah × V = Wh
Online calculator
Calculate Lithium Battery Capacity and Energy
Enter the values you already know. The calculator converts capacity, voltage, power, current, and operating time into a theoretical battery capacity or energy reference.
Planning estimate only.Use the battery's nominal voltage and rated capacity. The result does not replace cell datasheets, charger specifications, BMS design, or final engineering validation.
Inputs
Choose a calculation path
How it works
How Do You Calculate Lithium Battery Energy?
Battery energy is commonly estimated by multiplying rated capacity in amp-hours by nominal voltage. If the capacity is listed in milliamp-hours, divide it by 1,000 first.
V
Nominal voltage
Nominal voltage is the reference voltage used to convert capacity into an approximate energy value.
Wh
Energy
Wh and kWh make it easier to compare batteries with different voltage and capacity combinations.
Capacity in Ah = Capacity in mAh ÷ 1,000
Energy in Wh = Capacity in Ah × Nominal Voltage in V
Energy in kWh = Energy in Wh ÷ 1,000Understand the result
Battery Capacity vs. Battery Energy
A higher mAh rating does not always mean more stored energy when voltage is different. Watt-hours provide a more useful comparison between batteries with different electrical characteristics.
| Term | Meaning | Common unit | What it helps estimate |
|---|---|---|---|
| Battery capacity | The rated amount of charge available from the battery. | mAh or Ah | Current and operating time |
| Battery energy | The approximate electrical energy calculated from capacity and voltage. | Wh or kWh | Power demand and total energy |
| Nominal voltage | A reference voltage used for battery energy conversion. | V | Capacity-to-energy calculation |
Unit conversion
Common Lithium Battery Capacity and Energy Conversions
The calculator keeps the unit conversion visible so users can check how the result was produced.
1
mAh to Ah
Ah = mAh ÷ 1,000
2
mAh to Wh
Wh = mAh × V ÷ 1,000
3
Wh to mAh
mAh = Wh × 1,000 ÷ V
4
Wh to kWh
kWh = Wh ÷ 1,000
For lithium battery packs
How to Calculate Battery Pack Energy
Series and parallel configuration affect pack voltage and capacity in different ways. The advanced pack mode provides a basic nominal scaling reference before detailed pack engineering.
S
Series increases voltage
Pack nominal voltage is estimated as cell voltage multiplied by the number of cells in series.
P
Parallel increases capacity
Pack capacity is estimated as single-cell capacity multiplied by the number of parallel groups.
Wh
Energy combines both
Pack energy is calculated from pack voltage multiplied by pack capacity in amp-hours.
Pack Voltage = Cell Voltage × Series Count
Pack Capacity = Cell Capacity × Parallel Count
Pack Energy = Pack Voltage × Pack Capacity in AhPlanning accuracy
Nominal Energy Is Not the Same as Usable Energy
The basic formula gives a nominal energy estimate. The amount delivered to a device or system can be lower because operating conditions limit how much of the rated energy is available.
Rated capacity
Capacity is measured under specified test conditions and may not represent every real load profile.
Cutoff voltage
System cutoff settings affect how much of the nominal capacity can be used before the battery is disconnected.
System efficiency
Converters, wiring, BMS components, and device electronics can reduce delivered energy.
Temperature and age
Temperature, internal resistance, storage history, and aging can change practical performance.
Before using the result
Common Battery Capacity and Energy Calculation Mistakes
01
Using full-charge voltage
Use nominal voltage for energy comparison. Full-charge voltage is a different specification and should not be substituted automatically.
02
Comparing mAh alone
mAh does not show the complete energy picture when batteries have different nominal voltages.
03
Mixing cell and pack values
For a pack, distinguish single-cell capacity from complete pack capacity before calculating energy.
04
Ignoring system losses
Nominal energy is not a guarantee of usable energy at the device or system output.
05
Overstating precision
Use the result for planning and comparison, not as a substitute for battery testing or final engineering approval.
06
Skipping the datasheet
Confirm voltage, capacity, current limits, temperature range, and protection requirements from the selected battery documentation.
Where this helps
Capacity and Energy Planning for Battery-Powered Devices
The same calculation logic can support early battery planning for different device types. The final battery still needs to be checked against the device load, available space, connector, charging system, and protection requirements.
From calculation to battery design
Need help validating a custom battery requirement?
Share your voltage, capacity, current, dimensions, charging method, connector, protection requirements, and application conditions. ZERNE can review the early requirements for a lithium polymer or lithium battery pack project.
FAQ
Lithium Battery Capacity and Energy Questions
What is the difference between battery capacity and battery energy?
Battery capacity describes the amount of charge in mAh or Ah. Battery energy describes the approximate stored electrical energy in Wh or kWh and is calculated using capacity and nominal voltage.
How do I calculate battery energy from mAh?
Convert mAh to Ah by dividing by 1,000, then multiply Ah by nominal voltage. The formula is Energy in Wh = Capacity in Ah × Nominal Voltage in V.
What voltage should I use in a lithium battery energy calculation?
Use the battery or pack nominal voltage. Do not replace nominal voltage with maximum charge voltage unless the calculation specifically asks for a charge-voltage reference.
Does this calculator work for LiPo and 18650 batteries?
Yes. The calculator can be used for lithium polymer, LiPo, lithium-ion, and 18650 batteries when the rated capacity and nominal voltage are entered correctly.
Is calculated battery energy the same as usable energy?
No. The result is normally nominal energy. Usable energy can be lower because of cutoff voltage, system efficiency, temperature, aging, load profile, and other operating conditions.
How do I calculate the energy of a series-parallel battery pack?
First calculate pack voltage as cell voltage multiplied by series count and pack capacity as cell capacity multiplied by parallel count. Then multiply pack voltage by pack capacity in amp-hours.
Can a higher mAh battery always provide more energy?
No. Energy also depends on voltage. Batteries with different voltages should be compared using watt-hours rather than mAh alone.
What information is needed for a custom lithium battery?
A custom battery discussion normally needs voltage, capacity, continuous and peak current, dimensions, charging method, connector, protection requirements, operating temperature, application, and expected runtime.