Wh = Ah x V. To convert amp hours to watt hours, multiply the battery’s capacity in amp hours (Ah) by its nominal voltage (V).
In this formula, Wh stands for watt hours, Ah is amp hours, and V is the battery’s nominal voltage in volts. If your battery is rated in milliamp hours (mAh), divide by 1,000 to get amp hours before using the formula.
| Capacity (Ah) | Voltage (V) | Energy (Wh) |
|---|---|---|
| 1 | 12 | 12 |
| 5 | 12 | 60 |
| 10 | 24 | 240 |
| 50 | 48 | 2,400 |
| 100 | 51.2 | 5,120 |
| 200 | 51.2 | 10,240 |
| 280 | 384 | 107,520 |
| 600 | 51.2 | 30,720 |
How do you convert mAh to Wh for battery sizing?
To convert milliamp hours (mAh) to watt hours (Wh), use Wh = mAh x V / 1,000. For example, a 2,000 mAh battery at 3.7V: Wh = 2,000 x 3.7 / 1,000 = 7.4 Wh. Always check if the datasheet lists capacity in mAh or Ah.
Worked examples for amp hour to watt hour conversion
Example 1: A 100Ah battery at 12V: Wh = 100 x 12 = 1,200 Wh.
Example 2: A 200Ah battery at 51.2V: Wh = 200 x 51.2 = 10,240 Wh.
Example 3: A 280Ah battery at 384V: Wh = 280 x 384 = 107,520 Wh.
What mistake do people make when converting amp hours to watt hours?
The most common mistake is using the wrong voltage—such as the battery’s maximum, minimum, or charger voltage—instead of the nominal voltage. Another frequent error is confusing mAh with Ah; 1,000 mAh equals 1 Ah. If you use the wrong unit or voltage, your energy calculation will be off, which can lead to undersized or oversized systems.
Why does the amp hours to watt hours figure matter in battery procurement?
The watt hour figure tells you the total energy the battery can deliver at its nominal voltage. Procurement decisions—like matching batteries to inverters or load requirements—depend on this value. Remember, usable watt hours are lower than the rated value due to depth-of-discharge limits and system losses. Always check the specification and clarify whether the figure is gross or usable energy.
What should you do next?
Check your battery’s datasheet for capacity and nominal voltage, then run the calculation on your own figures to verify sizing before procurement.
Frequently asked questions
Is amp hour to watt hour conversion affected by temperature?
Yes, battery capacity in amp hours drops at low temperatures, so the calculated watt hours will be lower in cold environments. Always check the rated temperature condition on the datasheet.
Can I use the maximum or minimum voltage for amp hour to watt hour conversion?
No, always use the nominal voltage specified for the battery. Using maximum or minimum voltage will give you an inaccurate energy value.
How do I convert amp hours to watt hours for a battery bank with mixed voltages?
You must calculate watt hours for each string at its own nominal voltage, then sum the total Wh. Mixing voltages directly in the formula will give incorrect results.
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