How Many mAh Does a Power Bank Actually Need? (Plain-English Guide)
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A modern phone battery holds somewhere around 4,000 mAh. So a 10,000 mAh power bank should charge it two and a half times, right?
No. And that gap is the single most useful thing to understand before you order branded power banks for a campaign — because recipients absolutely notice when the math doesn't match the label.
Why a 10,000 mAh bank doesn't deliver 10,000 mAh
Energy gets lost in the transfer. Voltage conversion, heat, cable resistance — call it the efficiency tax. Real-world delivery from a power bank runs about 60–70% of the rated capacity. So:
- A 10,000 mAh bank delivers roughly 6,000–7,000 mAh of usable charge.
- Against a ~4,000 mAh phone, that's about 1.5 full charges, not 2.5.
That's not a defect. Every power bank on earth works this way. But if your branded bank says 10,000 and a recipient expects two and a half charges, they'll think it's cheap. Setting the expectation right — or just picking the right size — fixes it.
The size cheat sheet
Here's what each tier actually does, in charges, for a typical phone:
| Rated capacity | Real usable | Phone charges | Best for |
|---|---|---|---|
| 10,000 mAh | ~6,500 mAh | ~1.5 | The B2B sweet spot |
| 20,000 mAh | ~13,000 mAh | ~3 | Travel, power users, tablets |
| 26,800 mAh | ~17,000 mAh | ~4 | Heavy/multi-device (and the airline carry-on ceiling) |
For most promotional campaigns, 10,000 mAh is the one. It's enough to be genuinely useful — a full daily charge plus a buffer — without the bulk and cost of a 20,000. It also lands at a price that works for B2B gifting (around $13.50 at 250 units), which is why it's the most-ordered capacity we run.
The specs that matter more than mAh
Capacity is the headline, but these decide whether someone keeps the thing on their desk or in a drawer:
Output wattage. This is speed. An 18W+ bank with USB-C Power Delivery (PD) charges a phone in about an hour. A cheap 5W bank takes three. For a gift, fast matters more than huge — nobody's impressed by a 20,000 mAh brick that charges at a trickle.
USB-C, both ways. The bank should charge and be charged over USB-C. Recipients have largely ditched the old micro-USB cable. A bank that needs one feels dated the day it arrives.
MagSafe / Qi wireless if your audience is Apple-heavy. A magnetic bank that snaps to the back of an iPhone gets used constantly. It costs a few dollars more (~$14–18 at 250) and it's worth it for a tech crowd — clip-on convenience drives daily use.
Pass-through charging. Lets the bank charge a phone while it's itself plugged in. Small thing, genuinely handy, marks a quality unit.
Match the size to the audience
- Conference attendees, general staff → 10,000 mAh, USB-C, 18W. Done.
- Frequent travelers, field teams → 20,000 mAh. They'll burn through a 10K.
- Apple-ecosystem clients (tech, creative, finance) → 10,000 mAh MagSafe.
- Mass giveaway on a budget → 5,000 mAh slim. A top-up, but cheap and pocketable.
A quick word on shipping and safety
Lithium batteries ship under UN38.3 rules — it's a real certification, and any legit supplier provides the documentation. It mostly affects international air freight and lead time (budget 14–21 days for production on tech, longer than printed goods). Banks above 27,000 mAh hit airline carry-on limits, which is the other reason almost nobody orders past 26,800 for a gift.
FAQs
Is a 10,000 mAh power bank enough?
For most people, yes — it delivers about 6,000–7,000 mAh of real charge, or roughly 1.5 full phone charges, which covers a long day plus a buffer. It's the sweet spot for promotional gifts: useful without the bulk or cost of a 20,000 mAh unit.
Why doesn't my power bank fully charge my phone the number of times it should?
Because of the efficiency tax. Voltage conversion and heat eat 30–40% of the rated capacity, so a 10,000 mAh bank delivers around 6,500 mAh of usable energy. This is normal for every power bank — the rating measures the cells, not what reaches your phone.
What's more important, capacity or charging speed?
For a gift, speed usually wins. An 18W+ USB-C Power Delivery bank charges a phone in about an hour and gets used daily; a high-capacity but slow (5W) bank feels frustrating and gets shelved. Aim for 10,000 mAh and 18W PD rather than chasing raw mAh.
Should I get MagSafe power banks for a promotional campaign?
If your audience is Apple-heavy, yes. A magnetic bank that snaps onto an iPhone gets used far more than one that needs a cable. It runs a few dollars more (~$14–18 at 250 units) but the daily-use rate — and the brand exposure that comes with it — more than justifies it.
How big a power bank can you take on a plane?
Airlines generally cap carry-on power banks around 27,000 mAh (100 watt-hours). That's why 26,800 mAh is the practical ceiling for travel gifts — above it, recipients can't fly with it.
Picking power banks for a campaign? Tell us the audience and quantity and we'll spec the right capacity, wattage, and connector — not just the biggest number on the label.
Related: Power banks vs wireless chargers · Custom power banks buyer guide · Tech & gadgets complete guide
Capacity math based on standard 60–70% power-bank efficiency; pricing from openXpromo catalog at 250-unit MOQ.