What is Battery Capacity (mAh)?
Battery capacity, measured in milliampere-hours (mAh), indicates how much electrical charge a battery can store. The higher the mAh number, the more energy the battery holds and – all else being equal – the longer it will last before needing a recharge. It is the primary specification used to compare smartphone batteries and portable chargers.
However, mAh alone does not tell the whole story. Because it only measures charge without accounting for voltage, comparing batteries at different voltages requires a different unit: Wh (watt-hours). Understanding both units helps you make genuinely informed purchasing decisions.
In-Depth
What mAh Means in Practice
mAh stands for milliampere-hours, indicating how many milliamps of current a battery can deliver for one hour. A 5,000 mAh battery can theoretically supply 500 mA for 10 hours, or 1,000 mA for 5 hours. Today’s smartphones typically have batteries rated between 4,000 and 5,500 mAh, with larger batteries generally correlating to longer screen-on time – though software optimization, display type, and chipset efficiency also play significant roles.
mAh vs. Wh: Why It Matters
| Unit | Measures | Formula |
|---|---|---|
| mAh | Charge (current x time) | Capacity expressed in current terms |
| Wh | Energy (power x time) | mAh x Voltage / 1,000 |
Because mAh ignores voltage, you cannot directly compare a 10,000 mAh power bank (typically 3.7V internal cells) to a 5,000 mAh phone battery (typically 3.85V) by simply dividing. A 10,000 mAh power bank stores 37 Wh (10,000 x 3.7 / 1,000), while the phone battery stores 19.25 Wh (5,000 x 3.85 / 1,000). Wh provides an apples-to-apples energy comparison. Portable power stations are rated in Wh precisely because they serve devices at many different voltages.
Calculating Real-World Charge Counts
When estimating how many times a power bank can charge your phone, you must account for conversion efficiency – typically 70–85% due to heat loss during voltage conversion:
Example: A 10,000 mAh / 37 Wh power bank charging a 5,000 mAh / 19.25 Wh phone at 80% efficiency: 37 x 0.80 / 19.25 = approximately 1.5 full charges. The headline “10,000 mAh” might suggest 2 charges, but real-world physics reduce that number.
How to Choose
1. Match Capacity to Your Usage
For daily phone top-ups, a power bank with 2–3 times your phone’s battery capacity is a good starting point. A 5,000 mAh phone pairs well with a 10,000–15,000 mAh power bank. For multi-day trips or emergency preparedness, consider 20,000 mAh or more.
2. Compare in Wh, Not Just mAh
When evaluating portable power stations or comparing batteries across different device types, Wh is the more accurate comparison metric. It also matters for air travel: airlines typically allow batteries up to 100 Wh without restriction and up to 160 Wh with carrier approval.
3. Factor in Charging Speed
A large-capacity battery takes longer to recharge. Look for power banks that support PD charging or fast charging for both input (recharging the power bank) and output (charging your devices). Check the input wattage – a 20,000 mAh bank with only 10W input will take most of a day to recharge, while one supporting 30W+ input finishes in a few hours.
The Bottom Line
Battery capacity in mAh is the most common specification you will encounter when shopping for phones, earbuds, and power banks, but it is an incomplete measure of actual usable energy. Always consider voltage and conversion efficiency when estimating real-world performance, and use Wh for cross-device comparisons. Choose a capacity that matches your daily needs and travel habits, and pair it with fast-charging support so you spend less time tethered to a wall outlet.