Battery Runtime Calculator
Estimate how long a battery can power a device based on battery capacity, voltage, power consumption and system efficiency.
Calculate battery energy, usable energy and estimated runtime in hours and minutes.
Calculate Battery Runtime
Enter the battery specifications and device power consumption.
Battery Runtime Results
Battery Runtime Summary
Battery Capacity
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Battery Voltage
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Power Consumption
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Estimated Runtime
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How Battery Runtime Is Calculated
Battery runtime depends on the amount of energy stored in the battery and the amount of power consumed by the connected device.
When battery capacity is provided in amp-hours, the battery's approximate energy is calculated by multiplying amp-hours by voltage.
Battery Energy (Wh) = Battery Capacity (Ah) × Voltage (V)
Runtime (hours) = Usable Battery Energy (Wh) ÷ Device Power (W)
The calculator applies the selected system efficiency to estimate the usable energy available to the device.
Amp-Hours vs. Watt-Hours
Amp-hours (Ah) measure electrical charge capacity, while watt-hours (Wh) represent energy capacity. Voltage is needed to convert amp-hours into watt-hours.
For example, a 12 V battery rated at 100 Ah has an approximate nominal energy capacity of 1,200 Wh.
The actual usable energy can be lower depending on battery chemistry, discharge limits, temperature, age, load and other operating conditions.
Battery Runtime Example
Suppose a battery has a capacity of 100 Ah at 12 V and powers a device consuming 60 W.
Battery energy = 100 Ah × 12 V = 1,200 Wh.
At 100% efficiency, the theoretical runtime is: 1,200 Wh ÷ 60 W = 20 hours.
Real-world runtime may be lower because batteries and power systems are not perfectly efficient.
Factors That Affect Battery Runtime
The calculated runtime is an estimate. Actual battery performance can vary because of several factors.
| Factor | Effect on Runtime |
|---|---|
| Device Power | Higher power consumption generally reduces runtime. |
| Battery Age | Older batteries may have reduced effective capacity. |
| Temperature | Extreme temperatures can affect battery performance. |
| System Efficiency | Conversion losses reduce the energy delivered to the device. |
| Discharge Limits | Some batteries should not be fully discharged. |
| Load Variation | Devices with changing power demands may have different runtime than a constant-load calculation. |
Frequently Asked Questions
How do I calculate battery runtime?
Convert the battery capacity into watt-hours by multiplying amp-hours by voltage, then divide the usable energy by the device's power consumption in watts.
How long will a 100 Ah battery last?
It depends on the battery voltage and the power consumed by the connected device. A 100 Ah battery at 12 V contains approximately 1,200 Wh of nominal energy before efficiency and discharge limits.
What is the difference between Ah and Wh?
Ah measures electrical charge capacity, while Wh measures energy. Voltage connects the two measurements: Wh = Ah × V.
Why is my actual battery runtime lower?
Real-world runtime can be affected by efficiency losses, battery age, temperature, discharge limits, changing loads and the battery's actual available capacity.
Can I use mAh instead of Ah?
Yes. The calculator supports both Ah and mAh. A capacity given in mAh is converted to Ah before calculating battery energy.
Does higher battery voltage increase runtime?
Voltage affects the amount of energy represented by a given amp-hour rating. Runtime ultimately depends on total usable watt-hours and device power consumption.