How to Choose a Power Bank
Capacity is only half the story. The right power bank also matches your devices on wattage and ports, stays within airline limits, and is genuinely safe. Here is how to choose.
Power banks look interchangeable, but the wrong one charges your phone painfully slowly, will not power your laptop at all, or gets confiscated at airport security. Choosing well means looking past the headline capacity number to four things that actually matter: how much energy it stores, how fast it can output, which ports and protocols it speaks, and whether it is safe and airline-legal. This guide walks through each so you buy once and buy right.
Key takeaways
- Capacity (mAh) tells you how many charges; Wh is what airlines care about.
- Output wattage and USB PD decide how fast it charges — and whether it can power a laptop.
- Most carry-ons are limited to 100Wh (about 27,000 mAh) without airline approval.
- Buy reputable, certified units — cheap unbranded cells are a real fire risk.
Capacity: mAh and Wh
Capacity is usually advertised in milliamp-hours (mAh). As a rough guide, a 10,000 mAh bank gives a modern phone around two full charges, and 20,000 mAh gives three to four (real-world figures are lower because conversion loses 20–35% of the rated capacity). The other unit, watt-hours (Wh), measures actual energy and is what airlines regulate. You can convert: Wh = mAh × voltage ÷ 1000, with most banks at 3.7V. So a 20,000 mAh bank is about 74Wh.
| Capacity | Approx. Wh | Good for |
|---|---|---|
| 5,000 mAh | ~18 Wh | One phone top-up, pocketable |
| 10,000 mAh | ~37 Wh | 1–2 phone charges, daily carry |
| 20,000 mAh | ~74 Wh | Multiple devices, travel |
| 26,800 mAh | ~99 Wh | Max for most airlines; tablets/laptops |
Output wattage and Power Delivery
Capacity decides how much you can charge; output wattage decides how fast. A phone fast-charges at roughly 18–30W, a tablet a little more, and laptops need 45–100W. Look for USB Power Delivery (PD) — the standard that negotiates higher voltages safely — and check the rated wattage per port. To power a laptop you need a USB-C PD output of at least 45W, ideally 60–100W. A bank with huge capacity but only 10W output will trickle-charge everything. See USB-C explained for how PD works.
Watch the per-port split. A bank may advertise "65W total" but split it across ports, so charging two devices at once halves the speed each gets. Check the per-port figures, not just the headline total.
Ports and cables
Match the ports to your devices. USB-C is now the standard for both input (recharging the bank) and high-speed output, and a USB-C PD port is essential for laptops and fast phone charging. A spare USB-A port is handy for older cables and accessories. Some banks include a built-in cable, which is convenient but cannot be replaced if it frays. Prefer USB-C in and out so a single cable type covers everything — and so you can recharge the bank quickly itself.
Airline carry-on limits
This catches travellers out constantly. Lithium power banks must go in carry-on, never checked luggage, per international aviation rules. Most airlines permit banks up to 100Wh freely (about 27,000 mAh at 3.7V), allow 100–160Wh only with airline approval and typically a two-unit limit, and ban anything above 160Wh. This is exactly why a "26,800 mAh" capacity is so common — it sits just under the 100Wh threshold. Check the Wh rating printed on the bank before you fly; if it is missing, security may refuse it.
Safety and quality
Lithium cells store a lot of energy, and poorly made banks can overheat or, rarely, catch fire. Buy from reputable brands, look for safety certifications (such as UL or CE marks) and avoid suspiciously cheap, unbranded units claiming impossible capacities. Good banks include protection circuitry against overcharging, over-discharging and short circuits. Stop using any bank that swells, gets very hot or is physically damaged, and never charge devices under a pillow or duvet. Microsoft and device makers warn against using uncertified chargers and cells for exactly these reasons.
Match it to your devices
Decide what you actually need to charge. For a phone-only daily carry, a 10,000 mAh PD bank is light and plenty. For travel with a phone and tablet, 20,000 mAh at 30W+ covers a day. For a laptop, insist on USB-C PD of 60W or more and capacity near the 100Wh airline ceiling. If your goal is simply to make your phone last longer day to day, also read how to extend phone battery life before buying a bigger bank than you need.
Quick picks by use
Everyday phone: 10,000 mAh, USB-C PD, ≤20W — small and pocketable. Travel multi-device: 20,000 mAh, 30–65W, dual USB-C ports. Laptop power: 24,000–26,800 mAh, 65–100W USB-C PD, under 100Wh for flights. Across all three, prioritise a known brand and clear safety marks over a few extra mAh from an unknown seller.
A few features separate a merely adequate bank from a genuinely good one. Pass-through charging lets the bank charge a device while it is itself being recharged, handy on a single wall socket overnight. USB-C input speed matters as much as output: a bank that recharges at 30W or more is ready again in a couple of hours, whereas a slow 10W input can take all night for a large cell. A small display or LED ring showing exact percentage beats four vague dots when you are deciding whether it will last the day. And weight is real — a 26,800 mAh bank can weigh close to half a kilogram, so do not buy more capacity than you will actually carry.
Finally, think about charging standards beyond PD. Some phones use proprietary fast-charging that a generic bank will not fully match, falling back to standard PD speeds — usually fine, but worth knowing. For Apple devices, a USB-C PD bank fast-charges modern iPhones well; for laptops, confirm the wattage your specific machine needs, as thin-and-light models charge happily at 30–45W while performance laptops may want 90W or more. Buying the right wattage class the first time is the difference between a bank that tops up your laptop and one that merely slows its battery drain.
Frequently asked questions
What capacity power bank do I need?
For a phone, 10,000 mAh gives one to two charges and stays pocketable; 20,000 mAh suits travel with several devices. For a laptop, aim near 24,000–26,800 mAh. Remember real-world output is 20–35% below the rated mAh because of conversion losses, so buy a little more than the math suggests.
Can I take a power bank on a plane?
Yes, but only in carry-on, never checked luggage. Most airlines allow banks up to 100Wh (about 27,000 mAh) freely, 100–160Wh with prior approval, and ban anything larger. Check the Wh rating printed on the bank before you fly, as security may refuse one without a visible rating.
What is USB Power Delivery and do I need it?
USB Power Delivery (PD) is the standard that lets a charger and device safely negotiate higher power for fast charging. You need PD to fast-charge modern phones and to power laptops at all. Look for a USB-C PD port rated at 45W or more if a laptop is on your list.
Are cheap power banks safe?
Reputable, certified power banks are safe, but very cheap unbranded units — especially ones claiming impossible capacities — can overheat or catch fire. Buy known brands with safety marks like UL or CE and built-in protection circuitry, and stop using any bank that swells, overheats or is damaged.
Sources & further reading
- Apple Support — Use USB-C and charging accessories safely
- FAA PackSafe — Lithium batteries and power banks
- USB-IF — USB Power Delivery
This guide is independently produced. We reference primary documentation from device makers and security authorities (NIST, CISA). Tudug is reader-supported and may earn from ads.