Converting watt-hours (Wh) to milliampere-hours (mAh) requires factoring in the battery’s voltage. The formula is: mAh = (Wh × 1000) ÷ Voltage. For example, a 10Wh battery at 5V equals 2000mAh. Voltage is critical because mAh measures charge capacity, while Wh represents energy—so neglecting voltage leads to inaccurate conversions, especially when comparing lithium-ion (3.7V) vs. lead-acid (12V) systems.
How to Convert Wh to mAh: Formula and Calculator
What’s the formula for converting Wh to mAh?
To convert Wh to mAh, divide watt-hours by voltage (V), then multiply by 1000: mAh = (Wh ÷ V) × 1000. This accounts for energy (Wh) and voltage (V) to calculate charge capacity. For instance, 24Wh at 12V equals 2000mAh. Pro Tip: Use a multimeter to confirm voltage if unsure—incorrect values skew results.
⚠️ Warning: Assuming 3.7V for all lithium batteries? No! LiFePO4 cells run at 3.2V—using 3.7V inflates mAh by 15%, leading to runtime miscalculations.
Wh measures energy (voltage × current × time), while mAh quantifies charge capacity. Since energy depends on voltage, omitting it makes conversions invalid. Imagine pouring water (energy) into two differently sized buckets (voltage levels)—their “full” marks (mAh) differ. A 100Wh solar generator at 24V equals ~4167mAh, but at 5V, it’s 20,000mAh. Always include voltage. Pro Tip: For USB power banks listed in mAh, multiply by 3.7V (nominal lithium voltage) to estimate Wh.
| Voltage (V) | 10Wh (mAh) | 50Wh (mAh) |
|---|---|---|
| 3.7 | 2,703 | 13,514 |
| 12 | 833 | 4,167 |
| 24 | 417 | 2,083 |
Why does voltage matter in Wh to mAh conversion?
Voltage directly impacts mAh calculations because it determines how much energy each amp-hour delivers. Higher voltage reduces mAh for equivalent Wh, while lower voltage inflates mAh. For example, 50Wh at 12V is ~4167mAh, but 50Wh at 5V becomes 10,000mAh.
Think of voltage as water pressure in a hose. Higher pressure (voltage) allows less water (charge) to achieve the same energy output. Without voltage, comparing mAh across devices is like comparing hose lengths without knowing pressure. This explains why a 20,000mAh power bank at 3.7V (74Wh) lasts longer on a phone than a 20,000mAh 12V battery (240Wh)—it’s actually six times more energy. Pro Tip: Check device specs—laptops often use 19V, while drones run on 11.1V. Use the correct voltage for accurate runtime estimates.
Can you convert Wh to mAh without voltage?
No—voltage is essential for accurate Wh-to-mAh conversions. Without it, the calculation lacks energy context. For instance, 100Wh could equal 27,027mAh at 3.7V or 8,333mAh at 12V. Always verify voltage via battery labels, spec sheets, or multimeters.
⚠️ Critical: Guessing voltage for DIY projects? Measure it! A 0.5V error on a 10Wh battery causes a 17% mAh miscalculation.
Wh-to-mAh conversions require voltage like a GPS needs coordinates. Imagine two 50Wh batteries: a 3.7V smartphone pack (13,514mAh) versus a 12V motorcycle battery (4,167mAh). Without voltage, they’d seem equivalent in mAh, but their real-world applications differ vastly. Why does this happen? Because Wh = V × Ah, so removing voltage breaks the relationship. Pro Tip: For common devices, memorize voltages: USB=5V, laptops=12-20V, EVs=300-800V.
How does battery chemistry affect Wh/mAh conversions?
Battery chemistry determines nominal voltage, which directly impacts conversions. Lithium-ion (3.7V), LiFePO4 (3.2V), and lead-acid (2V/cell) have unique voltages. A 100Wh LiFePO4 battery (32V system) equals 3125mAh, while the same Wh in lithium-ion (21.6V) equals ~4630mAh.
Take e-bike batteries: a 36V 10Ah (360Wh) lithium-ion pack converts to 10,000mAh, but a 48V 7.5Ah (also 360Wh) LiFePO4 system is 7,500mAh. Although their energy is identical, their charge capacities differ by 25% due to voltage variance. Pro Tip: When replacing batteries, match both voltage and chemistry to avoid BMS compatibility issues. For example, substituting LiFePO4 for lithium-ion might require recalculating mAh needs by 13%.
| Chemistry | Voltage | 100Wh = mAh |
|---|---|---|
| Li-ion | 3.7 | 27,027 |
| LiFePO4 | 3.2 | 31,250 |
| Lead-acid | 12 | 8,333 |
What are real-world examples of Wh to mAh conversions?
Common applications include power banks and EV batteries. A 37Wh smartphone battery at 3.7V is 10,000mAh, while a 1000Wh EV battery at 400V converts to 2,500mAh. Higher voltage systems yield lower mAh despite greater energy capacity.
Consider solar generators: a 500Wh unit at 12V equals ~41,667mAh, sufficient to recharge a 3000mAh phone 13 times. But what if it’s 24V? The mAh drops to 20,833, but total energy remains the same. This paradox highlights why voltage awareness is crucial. For example, confusing 12V and 24V systems could lead someone to underestimate a battery’s true capacity by 50%. Pro Tip: Label converted mAh with voltage (e.g., 20,000mAh @ 5V) to prevent misunderstandings.
Redway Battery Expert Insight
Accurate Wh-to-mAh conversions are vital for matching batteries to devices. At Redway Battery, we emphasize using precise voltages—like 3.2V for LiFePO4 cells—to calculate true mAh. Our modular LiFePO4 systems include voltage displays, ensuring users avoid conversion errors when sizing solar storage or EV packs for optimal performance and longevity.
FAQs
Marketing—higher mAh numbers seem impressive, but Wh reflects true energy. A 20,000mAh bank at 3.7V is 74Wh, while the same mAh at 5V is 100Wh. Always check voltage.
Can I use Wh and mAh interchangeably?
No—Wh measures energy, mAh measures charge. A 10,000mAh battery at 5V is 50Wh, but at 3.7V, it’s 37Wh. Voltage bridges the two units.
How does temperature affect Wh/mAh calculations?
Cold reduces voltage—a 3.7V Li-ion cell at 0°C might drop to 3.3V, increasing mAh by 12% for the same Wh. Always measure voltage under operating conditions.
How to Convert Watts to Amps or Amps to Watts or Volts to Watts
