Wh = Ah x V. To convert amp hours to watt hours, multiply the amp hour (Ah) rating by the nominal voltage (V) of the battery. For milliamp hours (mAh), use Wh = mAh x V / 1000.
In this formula, Wh stands for watt hours (the total energy capacity), Ah is amp hours (the charge capacity), mAh is milliamp hours (1 Ah = 1,000 mAh), and V is the nominal voltage of the battery. Use the nominal voltage listed on the battery specification, not the maximum or minimum.
| Capacity (Ah) | Voltage (V) | Energy (Wh) |
|---|---|---|
| 2.5 | 3.2 | 8.0 |
| 10 | 12.8 | 128.0 |
| 20 | 12.8 | 256.0 |
| 50 | 24 | 1,200.0 |
| 100 | 12.8 | 1,280.0 |
| 100 | 51.2 | 5,120.0 |
| 200 | 51.2 | 10,240.0 |
| 280 | 384 | 107,520.0 |
How do you convert amp hours to watt hours for a real battery?
To convert amp hours to watt hours for a real battery, multiply the amp hour rating by the nominal voltage. For example, a 100Ah battery at 51.2V: 100 x 51.2 = 5,120Wh.
For a 200Ah battery at 12.8V: 200 x 12.8 = 2,560Wh.
If the battery is rated in mAh, such as 2,600mAh at 3.7V: 2,600 x 3.7 / 1,000 = 9.62Wh.
What is the most common mistake when converting Ah to Wh?
The most common mistake is using the wrong voltage or confusing amp hours (Ah) with milliamp hours (mAh). Using the wrong voltage can understate or overstate the actual energy by a factor of two or more, which can lead to under-sizing or overpaying for battery systems. Always use the nominal voltage from the specification sheet, and if the capacity is in mAh, divide by 1,000 to get Ah before converting.
Why does the amp hours to watt hours conversion matter in procurement?
The amp hours to watt hours conversion matters because procurement decisions are made based on energy (Wh or kWh), not just charge (Ah). If you specify a battery system by Ah without considering voltage, you risk buying a system that cannot deliver the required energy, or you may overpay for excess capacity. This conversion is essential for comparing offers, calculating usable energy after depth-of-discharge limits, and defending your sizing decision to management.
How do you check a supplier’s watt hour calculation?
To check a supplier’s watt hour calculation, ask for the amp hour and nominal voltage figures, then multiply them yourself. If the supplier quotes only Ah, request the voltage and do the calculation. If the supplier quotes only Wh, ask for the underlying Ah and V so you can verify the math. This prevents misunderstandings and ensures you are comparing like with like.
Before placing an order, run the amp hours to watt hours calculation on your own specification to confirm the system will meet your energy requirements.
Frequently asked questions
Is amp hour to watt hour conversion the same for all battery chemistries?
Yes, the formula Wh = Ah x V applies to all battery chemistries. The only difference is the nominal voltage, which varies by chemistry. For example, LiFePO4 cells are typically 3.2V, while lead-acid cells are 2V or 12V.
What if my battery is rated in mAh instead of Ah?
If your battery is rated in mAh (milliamp hours), divide the mAh value by 1,000 to get Ah before using the formula. For example, 2,000mAh = 2Ah.
Why do some suppliers only quote Ah and not Wh?
Some suppliers quote only Ah because it is a direct measure of charge, but energy (Wh) is what determines how long a battery can power a load. Always ask for both Ah and nominal voltage to calculate Wh yourself.
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