Batteries are not solely measured in kWh because kWh ignores voltage, which is a crucial factor in understanding a battery's performance. While kWh provides a nominal measure of capacity, Ampere-hours (Ah) allow for voltage considerations.
Here's a breakdown:
Understanding Battery Measurements
To fully understand why both kWh and Ah (and voltage) are important, let's clarify what they represent:
| Metric | Description | Units |
|---|---|---|
| Voltage (V) | The electrical potential difference, essentially the "push" behind the electricity flow. | Volts |
| Ampere-hours (Ah) | The amount of electrical charge a battery can deliver over one hour. | Ah |
| Kilowatt-hours (kWh) | The amount of energy a battery can store or deliver. This is power (kW) multiplied by time (hours). | kWh |
The Importance of Voltage
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Voltage and Compatibility: Batteries must provide the correct voltage for the device they are powering. A 12V device won't work with a 6V battery, even if the 6V battery has a higher Ah rating.
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Power Calculation: The power (in Watts) delivered by a battery is calculated by multiplying Voltage (V) by Current (Amps, derived from Ah). Therefore, voltage is integral to understanding a battery's power output at any given time.
Why Ah is Also Important
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Direct Indication of Charge Capacity: Ah gives a more direct indication of how long a battery can supply a certain amount of current.
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Ease of Calculation: It's easier to calculate run time based on Ah, voltage, and the device's power consumption.
kWh is Still Relevant
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Total Energy Storage: kWh is the best metric for comparing the total amount of energy stored in batteries, regardless of voltage. This is particularly useful when comparing batteries of different voltages (e.g., comparing a low-voltage battery bank for solar storage with a high-voltage electric vehicle battery).
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Standard Unit for Energy: Because kWh is a standard unit for energy, it's easy to understand how much energy a battery holds in familiar terms.
In conclusion, while kWh is a useful measurement of a battery's total energy capacity, Ah and voltage are essential for understanding the battery's compatibility with a device and its ability to deliver power effectively. Handling capacity in Ah allows you to take voltage into consideration, which kWh ignores.
