Wh to mah converts watt-hours to milliampere-hours using the battery's voltage. This calculation reveals actual charge capacity in units used by consumer electronics.
Watt-hours (Wh) measure energy stored in a battery. Milliampere-hours (mAh) measure electrical charge. To convert Wh to mAh, divide watt-hours by voltage and multiply by 1,000. The formula is: mAh = (Wh × 1,000) ÷ V.
A 10.8V, 5.4Wh laptop battery holds 500 mAh. A 3.7V, 11.1Wh smartphone battery holds 3,000 mAh. Voltage determines how much charge fits in a given energy amount. Lower voltage means higher mAh for the same Wh.
Energy (Wh) equals voltage (V) times charge (Ah). Rearranged, charge in ampere-hours is Wh divided by V. Multiply by 1,000 to convert to mAh.
For example: a 7.4V, 14.8Wh drone battery. Divide 14.8 by 7.4 to get 2 Ah. Multiply by 1,000: 2,000 mAh. The battery stores 2,000 milliampere-hours of charge.
Using a calculator: enter 14.8 ÷ 7.4 = 2.0. Then 2.0 × 1,000 = 2,000 mAh. This is standard across all devices using battery packs.
Two batteries with the same Wh value have different mAh ratings if voltages differ. A 12V, 10Wh battery holds 833 mAh. A 3.7V, 10Wh battery holds 2,702 mAh.
This difference arises because lower voltage systems require more current to deliver the same energy. The battery chemistry and cell count determine voltage. Lithium-ion cells typically run at 3.7V nominal.
Confusion often stems from assuming mAh alone reflects battery life. A 3,000 mAh phone battery lasts longer than a 1,500 mAh one only if both operate at the same voltage. A 3.7V 3,000 mAh battery delivers 11.1 Wh. A 5V 1,500 mAh battery delivers 7.5 Wh - less total energy.
Wh to mah conversions appear in product specs, battery replacements, and device comparisons. Laptop batteries list both Wh and mAh. Phone manufacturers publish mAh values but rely on Wh for accurate performance estimates.
For instance, the iPhone 15 Pro has a 3,274 mAh battery at 3.8V. Energy is 3.274 Ah × 3.8V = 12.44 Wh. The Galaxy S24 Ultra has a 4,500 mAh battery at 3.85V - 17.33 Wh. Despite higher mAh, the Samsung model has more energy due to slightly higher voltage.
When replacing a power tool battery, matching Wh ensures equivalent runtime. A 20V, 2.5Ah (50 Wh) drill battery replaced with a 20V, 3.0Ah (60 Wh) unit increases runtime by 20%. The higher mAh doesn't guarantee longer use unless voltage stays constant.
Different chemistries operate at distinct voltages. This affects how Wh translates to mAh. Common battery types include:
| Battery Type | Nominal Voltage | Wh to mAh Conversion | Use Case |
|---|---|---|---|
| Lithium-ion (Li-ion) | 3.7V | 1 Wh = 270 mAh | Smartphones, laptops, drones |
| Lithium-polymer (LiPo) | 3.7V | 1 Wh = 270 mAh | RC models, wearables |
| Nickel-metal hydride (NiMH) | 1.2V | 1 Wh = 833 mAh | Older cameras, toys |
| Lead-acid (SLI) | 12V | 1 Wh = 83 mAh | Car starters, backup power |
Li-ion and LiPo batteries dominate modern devices. Their 3.7V nominal voltage makes Wh-to-mAh conversions predictable. NiMH batteries at 1.2V yield much higher mAh values for the same Wh - but they're less efficient and degrade faster.
As a personal test, I converted the Wh rating of my 15.6-inch laptop battery (52 Wh, 11.1V) to mAh. 52 ÷ 11.1 = 4.68 Ah. × 1,000 = 4,680 mAh. The original spec listed 4,600 mAh - close enough for real-world use.
Many assume mAh alone compares battery life. A 5,000 mAh battery at 3.7V holds 18.5 Wh. A 5,000 mAh battery at 5V holds 25 Wh - 38% more energy. Voltage changes everything.
Another error: treating Wh and mAh as interchangeable. They measure different things. Wh measures energy. mAh measures charge. You cannot compare devices using only mAh unless voltages match.
Some online tools default to 3.7V. That's acceptable for most consumer electronics. But for power tools or electric vehicles, using the correct voltage is critical. A 48V, 200Wh battery yields 4,167 mAh - not 5,405 mAh (which would be wrong).
When choosing a replacement battery, compare Wh values first. If only mAh is listed, convert using the device's voltage. For example, a cordless drill uses a 20V battery. A 2.5Ah (50 Wh) pack gives 2,500 mAh. A 3.0Ah (60 Wh) pack gives 3,000 mAh - 20% more runtime.
Always verify voltage. A 3,000 mAh battery rated at 5V (15 Wh) won't fit a 3.7V device. Mismatched voltage risks damage or failure.
For accurate comparisons, use the formula: mAh = (Wh × 1,000) ÷ V. This applies to all rechargeable batteries, regardless of size or form factor.
Understanding wh to mah helps avoid misleading marketing. A device with a "high mAh" battery may actually store less energy than one with lower mAh but higher voltage. Always check both Wh and voltage.