Choose the battery scope
Select Single cell for one LiPo pouch cell or one 18650 cell. Select Complete battery pack when using total pack values.
ZERNE Battery Calculation Tool
Lithium Battery Runtime Calculator
Estimate how long a LiPo battery, lithium polymer battery, 18650 cell, or lithium battery pack may power a device. Enter capacity, average current or load power, nominal voltage, and practical usage assumptions for a runtime planning estimate.
Current and load-power planningLiPo, 18650, and pack useIdeal and practical estimates
Runtimeplanning estimate
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Wh ÷ W = h
Online calculator
Estimate Your Lithium Battery Runtime
Enter the battery and load values you already know. Use average current for direct cell or device estimates, or use load power and nominal voltage for battery-pack planning.
Planning estimate only.Actual runtime depends on load variation, usable capacity, temperature, battery age, voltage drop, protection settings, and system efficiency. Confirm the result against the selected battery and device specifications.
Inputs
Choose a runtime calculation path
How to use it
How to Use the Lithium Battery Runtime Calculator
Choose the calculation path that matches the information available from your device, battery cell, or battery pack specification.
Choose the data you know
Use Capacity + Current for average current. Use Capacity + Power or Energy + Power when the device load is given in watts.
Set practical assumptions
Adjust usable capacity and system efficiency when cutoff limits or power conversion losses affect the usable result.
Review the estimate
Use the result to compare early battery options, then confirm the final choice with the selected battery and device specifications.
Calculation method
How Is Lithium Battery Runtime Calculated?
Runtime is estimated by comparing usable battery capacity or energy with the average load. The calculator keeps the theoretical result separate from the practical planning result.
Ah
Capacity and current
When average current is known, usable capacity in amp-hours is divided by the current in amps.
Wh
Capacity and power
Capacity is first converted into nominal energy using the battery’s nominal voltage, then compared with load power.
W
Energy and power
When battery energy is already known, watt-hours are divided by average load watts to estimate operating time.
Capacity in Ah = Capacity in mAh ÷ 1,000
Energy in Wh = Capacity in Ah × Nominal Voltage in V
Planning runtime = Usable energy in Wh ÷ Average load power in W
Usable energy = Nominal energy × Usable capacity × System efficiencyBattery type and scope
Use the Calculator for LiPo, 18650, and Battery Packs
The calculation method is shared, but the value entered must match the battery object you are evaluating: one cell or the complete pack.
| Battery type | What to enter | Important planning note |
|---|---|---|
| LiPo / lithium polymer battery | Rated capacity of one cell or the complete LiPo pack, plus average current or load power. | For high-load applications, use average operating current rather than the short-duration peak current. |
| 18650 lithium-ion cell | Capacity and nominal voltage of the individual 18650 cell when estimating single-cell runtime. | Do not use a complete pack’s capacity when calculating one cell. |
| Lithium battery pack | Total pack capacity, nominal pack voltage, and average device load. | Series connections increase voltage while parallel groups increase capacity and current capability. |
Practical conditions
Why Actual Battery Runtime Can Differ
A runtime formula is useful for early planning, but a real device rarely operates under perfectly stable laboratory conditions.
01
Average load and peak load
Startup, transmission, acceleration, or high-brightness events can temporarily increase demand beyond the average value.
02
Cutoff and BMS settings
A device or BMS may stop using the battery before all rated capacity has been delivered.
03
Temperature and battery age
Temperature, cycle history, internal resistance, and cell condition can change practical capacity and voltage behavior.
04
Converter and wiring losses
DC-DC converters, inverters, connectors, and cable resistance can reduce the energy reaching the device.
05
Cell and pack structure
Cell matching, parallel count, welds, wiring, BMS limits, and enclosure conditions affect complete pack performance.
06
Rated versus usable energy
Nominal capacity and energy are reference values, not a guarantee that the same amount reaches the device output.
Continue planning
From Capacity and Energy to Runtime
If you do not know the battery energy or need to convert between mAh, Ah, Wh, and kWh first, start with the capacity and energy calculator.
Where runtime planning helps
Battery Runtime Planning for Different Devices
The same planning logic can support early decisions for portable and connected products. The final battery still needs to match the device’s space, connector, charging method, protection system, and operating profile.
From runtime estimate to battery design
Need a Battery Built Around Your Runtime Target?
Share your target runtime, average or peak load, required voltage, available battery space, connector, charging method, and operating conditions. ZERNE can review the early requirements for a LiPo, 18650, or custom lithium battery pack.
FAQ
Lithium Battery Runtime Questions
What does a lithium battery runtime calculator calculate?
It estimates how long a LiPo battery, 18650 cell, or lithium battery pack may power a device based on its capacity or energy and the average load. The result is a planning estimate rather than a guaranteed operating time.
Can I use this calculator for a LiPo battery?
Yes. You can use it for a single LiPo cell or a complete LiPo battery pack. Enter the rated capacity of the same battery scope you are evaluating, and use the average current or load power of the device.
Can I use this calculator for an 18650 battery?
Yes. For a single 18650 cell, use the cell’s own rated capacity and nominal voltage. For an 18650 battery pack, use the total pack capacity and nominal pack voltage rather than the values of only one cell.
What is the difference between battery runtime and battery life?
Battery runtime describes how long the battery can power a device during one discharge period. Battery life or battery lifespan refers to how many cycles or how many years the battery may remain usable. This calculator estimates runtime only.
Should I use peak current or average current?
Use the average operating current for runtime planning. Peak current is important for checking the cell, BMS, connector, and wiring, but it usually should not be used as the continuous runtime current.
Why is actual runtime shorter than the calculator result?
Actual runtime may be lower because of changing load demand, battery cutoff settings, temperature, battery aging, voltage conversion losses, wiring resistance, and the difference between rated and usable capacity.
Do I need nominal voltage for every calculation?
No. Nominal voltage is required when you calculate runtime from capacity and load power. It is not required when battery energy in Wh is already known or when you use the capacity and average-current method.
Can this calculator select the right battery or BMS?
No. It provides an initial runtime reference only. Final battery and BMS selection must also consider peak current, charging requirements, temperature, dimensions, connectors, protection thresholds, and the selected cell or pack datasheet.