You might think that a 10,000mAh power bank could charge a 5,000mAh phone to 100 percent twice, but that’s not the case. If you want more power, be prepared to spend more and carry around a heavier brick. Unsurprisingly, the prices on most batteries goes up as capacity increases, and since batteries are physical storage units, size and weight go up with capacity as well. Larger batteries that can recharge laptops and tablets, or give phones multiple charges, can exceed 25,000mAh.
Smaller batteries, say those that can charge a smartphone to between 50 and 75 percent, tend to have a 5,000mAh capacity. Power bank manufacturers almost always list a battery’s capacity in milliamp hours, or mAh. According to the TSA, external batteries rated at 100Wh or less (which all of our recommendations are) can fly with you – just make sure you stash them in your carryon the next time you fly as they aren’t allowed in checked baggage. While you should still make sure a battery isn’t exposed to unnecessary stress like excessive heat, damage from drops or operating in freezing weather, battery packs are considered safe enough to bring on an airplane. To limit the danger, battery packs require internal mechanisms to limit things like voltage and pressure. One drawback you may have heard is the possibility of lithium ion batteries catching fire.
