mAh stands for milliampere-hour, and it measures how much electric charge a battery can store. A battery rated at 1,000 mAh can supply 1,000 milliamperes of current for one hour, or 500 milliamperes for two hours, or 100 milliamperes for ten hours. The higher the mAh number, the longer the battery can power a device before it needs recharging.
How mAh Translates to Battery Life
The math is straightforward: divide a battery’s mAh rating by the average current your device draws (in milliamperes), and you get an estimate of runtime in hours. A phone with a 5,000 mAh battery drawing an average of 250 mA would last roughly 20 hours. Drop the screen brightness and close background apps so the draw falls to 125 mA, and that same battery stretches to about 40 hours.
This is a simplified estimate. Real-world battery life depends on temperature, how fast the battery is being drained, and the age of the battery. Lithium-ion cells lose energy to heat during discharge, especially at high drain rates. Cold weather reduces the chemical reactions inside the cell, temporarily lowering its effective capacity. A battery that’s been through hundreds of charge cycles will hold less charge than it did when new, even if the label still says the same mAh number.
Typical mAh Ratings by Device
Knowing what’s “normal” helps you compare products. Wireless earbuds typically have tiny batteries in the range of 40 to 70 mAh per earbud, with a charging case that holds 300 to 600 mAh. Smartwatches generally sit between 200 and 600 mAh. Smartphones have seen a steady climb: in 2025, CNET tested 35 phones and found flagships ranging from Apple’s iPhone 17 Pro Max at 5,088 mAh to the OnePlus 15 at a massive 7,300 mAh. Tablets often land between 7,000 and 11,000 mAh.
A higher mAh number doesn’t automatically mean longer battery life, though. The iPhone 17 Pro Max topped CNET’s battery life rankings despite having a smaller battery than several competitors, because Apple’s processor and software used power more efficiently. The device’s power consumption matters just as much as the battery’s capacity.
Why mAh Doesn’t Tell the Whole Story
mAh measures electric charge, not total energy. To know how much energy a battery actually holds, you need to factor in voltage. The formula is simple: multiply mAh by voltage, then divide by 1,000, and you get watt-hours (Wh). A 5,000 mAh phone battery running at 3.7 volts stores 18.5 Wh. A 5,000 mAh laptop battery running at 11.1 volts stores 55.5 Wh, three times as much energy despite the identical mAh rating.
This is why laptops list their batteries in Wh rather than mAh. At higher voltages, mAh becomes misleading because it hides the voltage difference. When you’re comparing batteries that run at the same voltage (like two smartphones, both using 3.7V cells), mAh is a perfectly fair comparison. When voltages differ, Wh is the only honest number.
The Power Bank Problem
If you’ve ever charged your phone from a 10,000 mAh power bank and wondered why it didn’t deliver nearly as many charges as expected, there’s a concrete explanation. The 10,000 mAh rating refers to the capacity of the internal battery cells, which operate at about 3.7 volts. But USB output runs at 5 volts. Converting from 3.7V to 5V reduces the usable capacity right away:
- Voltage conversion: 10,000 mAh at 3.7V equals 37 Wh of stored energy. At the 5V output, that becomes 7,400 mAh.
- Circuit efficiency loss: The electronics that boost the voltage are roughly 82% efficient, burning the rest as heat. That brings the real output down to about 6,068 mAh.
So a “10,000 mAh” power bank realistically delivers around 6,000 mAh to your phone. This isn’t a scam. Manufacturers are required to print a “rated capacity” alongside the nominal capacity, and if you check the fine print on the label, you’ll usually find that lower number. A 5,000 mAh phone would get just over one full charge from a 10,000 mAh power bank, not two.
How to Use mAh When Shopping
For phones, earbuds, and other gadgets that all use similar voltage cells, comparing mAh is a quick and useful shortcut. A phone with 6,500 mAh will generally outlast one with 4,500 mAh, assuming similar processors and screens. For power banks, look at the rated capacity (in mAh at 5V) or the Wh figure rather than the headline number. For laptops and power stations, ignore mAh entirely and compare Wh.
Keep in mind that battery capacity is just one variable. Software optimization, screen brightness, cellular signal strength, and processor efficiency all shape how long your device lasts on a charge. Two phones with identical 5,000 mAh batteries can deliver wildly different screen-on times. The mAh number tells you how big the fuel tank is. It doesn’t tell you how fuel-efficient the engine is.