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01Decide how many charges you actually need
To choose a power bank, start with capacity: work out how many full phone charges you need between wall outlets, then buy the smallest bank that covers it. Bigger isn't free. Every extra 10,000 mAh adds weight, bulk and hours of recharge time.
The number on the box (mAh) is the capacity of the cells inside, not what reaches your phone. Voltage conversion, heat and the bank's own circuitry eat a chunk of it, so over a cable you get roughly two-thirds. Set your bank size and phone below to see the real figure.
| Capacity | Roughly | Good for | Trade-off |
|---|---|---|---|
| 5,000 mAh | About 1 charge | Evenings out, a top-up in your pocket | Won't rescue a dead phone twice |
| 10,000 mAh | 1.5–2 charges | Daily carry, commuting, weekend trips | The best size-to-charge ratio |
| 20,000 mAh | 3–4 charges | Travel days, festivals, sharing with a friend | Noticeably heavier; slow to refill |
| 30,000 mAh and up | 5+ charges | Camping, tablets, power cuts | Can be over the 100 Wh airline line |
02Match the output to your phone's charging standard
Capacity decides how many charges. Output decides how long you stand next to the bank waiting. Look for the charging protocol printed on the box, not just the wattage.
| Your phone | What the bank needs | Watts worth paying for |
|---|---|---|
| iPhone with USB-C (15 and later) | USB Power Delivery (PD) on a USB-C port | 20W or more |
| Older iPhone with Lightning | USB-C PD plus a USB-C to Lightning cable | 20W or more |
| Samsung Galaxy | USB PD with PPS | 25W for most models; 45W helps on Ultra models |
| Google Pixel | USB PD with PPS | Check your model's spec page |
The PPS detail catches a lot of Galaxy owners. Without it, a Samsung phone charges at standard speed even from a high-watt bank. If you're unsure what your phone supports, our explainers on USB Power Delivery and PPS charging cover it in a few minutes.
Also check the input rating. A bank that recharges at 20W or more refills in an evening. One that only takes 10W from the wall can need most of a night at 20,000 mAh.
03Cable bank or magnetic snap-on?
This is the choice that shapes how you'll use it. Magnetic banks snap onto the back of an iPhone 12 or later (except the 16e), a Pixel 10 with built-in magnets, or any phone in a magnetic case, so you can keep using the phone while it charges.
Cable power bank
- About two-thirds of capacity reaches the phone
- Fastest charging with USB-C PD
- Charges earbuds, tablets and a second phone
Magnetic wireless bank
- No cable to snag in a pocket
- Loses more energy as heat, so fewer charges
- Needs magnets in the phone or the case
We'd pick a cable bank as your main one and a slim magnetic bank only if you're constantly topping up on the move. Most magnetic banks have a USB-C port too, so you can switch to the cable when you need every percent. If your Galaxy or older Android has no magnets, add a MagSafe-compatible case first. Our magnetic vs regular power bank comparison goes deeper.
04Ports, screens and the small stuff
- At least one USB-C port that works both ways (in and out). It means one cable for the bank, your phone and most earbuds.
- A percentage display beats four vague LEDs. You'll know whether 30% is enough for the day.
- Two outputs if you often charge a phone and earbuds at once. Expect the speed to split between ports.
- Pass-through charging lets the bank charge your phone while it's plugged in itself. Handy on a hotel nightstand with one outlet, but not every bank supports it.
- Low-current mode keeps small gadgets like earbuds or a watch charging when a normal bank would switch itself off.
Built-in flashlights, solar panels and wireless watch pads add cost and size. A solar panel the size of a phone only trickles power in direct sun, so treat it as a backup and buy one only if you genuinely camp off-grid.
05Will it fly, and will it fit?
Airlines measure batteries in watt-hours (Wh), and the line that matters is 100 Wh. At the usual 3.7V cell voltage, that's about 27,000 mAh. A 20,000 mAh bank is roughly 74 Wh and flies anywhere in your carry-on; a 30,000 mAh one usually lands just over the line. Plug any bank into our power bank flight checker, or read the full 2026 airline rules.
For pockets, 10,000 mAh is the practical ceiling. Thin aluminum and slim magnetic banks fit a jeans pocket; 20,000 mAh banks belong in a bag.
A daily 10,000, a travel 20,000 and two magnetic options. All sit comfortably under 100 Wh.
06The 30-second buying checklist
Once you own one, keep it alive longer by storing it half full in a cool place. Our guides on storing a power bank and how long power banks last cover the habits that matter.
Questions people ask
What size power bank should I buy?
10,000 mAh suits most people. It gives a typical phone about one and a half to two full charges by cable and still fits a pocket. Go to 20,000 mAh for long travel days or two devices, and only go bigger for camping or tablets.
Is a 20,000 mAh power bank too big?
Not for a bag. It's roughly 74 Wh, so it's allowed in carry-on luggage, and it gives three to four phone charges. It's heavy for a pocket, though, and takes several hours to refill unless it has a fast USB-C input.
What does PD mean on a power bank?
PD stands for USB Power Delivery, the fast-charging standard used by iPhones, Galaxy phones and Pixels over USB-C. A bank without it charges most modern phones at slow 5V speeds, however many watts the box claims.
Are magnetic power banks worth it?
They're worth it if you charge while using your phone, since there's no cable in the way. The trade-off is efficiency: wireless charging loses more energy as heat, so you get fewer charges than a cable bank of the same size, and the phone runs warmer.
Does a power bank need a high wattage to charge an iPhone fast?
An iPhone fast-charges from a USB-C PD source of 20W or more. Higher-watt banks won't hurt it, since the phone only draws what it can take, and they're useful if you also charge a tablet or laptop.