Battery energy can be measured in several ways, but one of the simplest methods is using milliamp-hours (mAh), particularly for smaller batteries. Here's a breakdown:
Measuring Battery Capacity using mAh
The milliamp-hour (mAh) rating indicates how much current a battery can supply for a specific duration. A higher mAh rating generally means the battery can power a device for a longer time.
The Constant Current Discharge Method
This method involves connecting the battery to a constant current load and measuring the time it takes for the battery to discharge fully.
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Procedure:
- Connect the battery to a device or circuit that draws a constant current.
- Monitor the voltage of the battery as it discharges.
- Record the time it takes for the battery voltage to reach its minimum acceptable level (the "cutoff voltage").
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Calculation: Battery Capacity (mAh) = Discharge Current (mA) x Discharge Time (hours)
For example, if a battery discharges at a constant current of 100mA for 10 hours, its capacity is 1000mAh.
Practical Considerations
- Constant Current Load: Maintaining a truly constant current can be challenging, so specialized electronic loads are often used for accurate measurements.
- Cutoff Voltage: The cutoff voltage varies depending on the battery type and the device it powers. Refer to the battery's datasheet for the recommended cutoff voltage.
- Temperature: Battery capacity can be affected by temperature. Testing should ideally be conducted at a consistent temperature.
Other Methods for Measuring Battery Energy
While mAh is common, other methods and units are also used:
- Watt-hours (Wh): A more accurate measure of battery energy, considering both voltage and current. Wh = (mAh/1000) x Voltage.
- Coulomb Counting: A sophisticated technique used in battery management systems (BMS) to track the flow of charge in and out of the battery.
