Gadgets & Devices
Capacity, charging speed, and ports decide whether a power bank is right for you. Here is how to read the specs and pick one without overpaying.
Pick a power bank by matching three specs to your devices: watt-hours (how much energy it stores), output wattage over USB-C Power Delivery (how fast it refills your phone or laptop), and input wattage (how fast the bank itself refills). For most people, a 10,000–20,000 mAh bank with a 30W+ USB-C PD port and USB-C fast input is the sweet spot. The rest of this guide shows you how to read those numbers so you neither overpay for a brick you leave at home nor buy something that dies before lunch.
The milliamp-hour (mAh) figure on the box is measured at the internal cell voltage, usually 3.6V or 3.7V. Your phone charges at 5V or 9V, so the number that actually matters is watt-hours (Wh), which you can compute yourself: Wh = mAh × 3.7 ÷ 1000.
That turns the marketing numbers into something honest:
Watt-hours are comparable across brands; raw mAh is not, because a bank rated at a higher cell voltage stores more energy per mAh. When two banks both say "20,000 mAh," check the Wh printed on the label (regulators require it) and compare those instead.
Stepping the cell's 3.7V up to 5V or 9V wastes energy as heat, and the bank's own control board draws some too. In practice you get roughly 60–70% of the rated capacity delivered to your device. So a 10,000 mAh bank (37 Wh) hands over closer to 22–26 Wh.
Put that against real phone batteries, which hold roughly 12–20 Wh (an iPhone 16 is around 14 Wh, a Galaxy S24 around 19 Wh, a Pro Max model closer to 17 Wh). That means a 10,000 mAh bank realistically gives you about 1.5 full phone charges, not the "three charges" some listings imply. Build in that buffer and you won't be caught short.
Output is measured in watts (volts × amps) and delivered over a charging standard. The one to prioritize is USB-C Power Delivery (USB PD), the universal standard that every recent phone, tablet, and USB-C laptop understands.
Here's what different devices actually pull:
For Samsung's fastest speeds, look specifically for PPS (Programmable Power Supply) support in the spec sheet — without it, a Galaxy falls back to slow charging even on a high-wattage bank.
People buy a huge 20,000 mAh bank that only outputs 5V/2.1A — that's 10W, roughly half of modern fast-charging speed. It technically works, but a "quick top-up before you leave" turns into an hour of waiting. Check the output rating (look for at least "PD 20W" or "PD 30W"), not just the capacity.
Also remember that multiple ports share a power budget. A bank advertised as 65W total might deliver 45W to one port but drop to 45W + 18W when you plug in a second device. If you plan to charge a laptop and a phone at once, read the per-port breakdown.
The overlooked spec is how fast the bank recharges. A budget model that only accepts 5–10W over an old micro-USB port takes 8–12 hours to refill a 20,000 mAh cell — miss an overnight charge and it's useless the next morning.
A bank with USB-C PD input at 30–65W refills the same 20,000 mAh in roughly 2–3 hours. To actually hit those speeds you need three things at once: a bank that accepts fast input, a wall charger that can supply it (a compact GaN USB-C PD charger is ideal), and a USB-C cable rated for the current. A slow charger or a thin cable throttles even a capable bank.
USB-C PD in and out is the baseline in 2026. A USB-A port is still handy for older cables and accessories, but don't buy a bank that only has USB-A — it can't charge a laptop and won't hit modern phone speeds.
A few extras worth paying for, and one to be skeptical of:
Watt-hours also govern what you can fly with. Under FAA and international (IATA) rules, power banks must travel in carry-on, never checked luggage, and:
This is exactly why 20,000 mAh (74 Wh) and 26,800 mAh (99 Wh) are the standard "travel" sizes — they sit just under the 100 Wh line. Anything advertised much larger will cause problems at the gate.
On weight, budget roughly 200g for a 10,000 mAh bank and 350–500g for a 20,000 mAh one. A bag you carry everywhere can absorb the weight; a jacket pocket wants the slim model.
Lithium cells are only as safe as the protection circuitry around them. Buy from an established brand (Anker, Ugreen, Baseus, INIU, Belkin) rather than an unbranded cell from the bargain bin — the difference is over-current, over-temperature, and short-circuit protection you can't see on the outside. Then treat it well: store it around 40–60% charge for long stretches rather than fully empty or full, keep it out of hot cars and direct sun (heat degrades cells fastest), and if the casing ever swells or the bank runs unusually hot, stop using it and recycle it at an e-waste drop-off rather than tossing it in the bin.
Realistically about 1.5 full charges for a modern phone, not the two or three some listings claim. After conversion losses you get roughly 60–70% of the rated capacity, and phone batteries have grown to 12–20 Wh. If you need two guaranteed full charges, step up to 20,000 mAh.
Yes, if it has a USB-C PD output of at least 45W — enough for a MacBook Air or most ultrabooks. For a 14- or 16-inch MacBook Pro or a gaming laptop you'll want 96–140W, which requires USB PD 3.1 and a 5A e-marked cable. A USB-A-only bank cannot charge a laptop.
No. Beyond your real needs it just adds weight, takes longer to recharge, and can cross the 100 Wh airline limit. A slim 10,000 mAh bank you actually carry beats a 30,000 mAh brick you leave on the counter.
PPS matters specifically for Samsung Galaxy "Super Fast Charging" — without it those phones charge slowly. Quick Charge is Qualcomm's standard used by some other Android phones. If you own an iPhone or a Pixel, plain USB-C PD is all you need.
Lena writes about phones, laptops, and gadgets for people who want good advice, not a spec-sheet recital. She's blunt about what's worth the money, patient with setup headaches, and a firm believer in making your devices last longer.
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