The Edit — Travel
Portable Charger mAh, Explained for a Day of Travel
A 10,000mAh power bank does not hold 2.5 charges for a 4,000mAh phone. It holds about 2, because the two numbers are measured at different voltages and about a fifth of the energy is lost on the way.
This guide is research-led: we have not handled these units ourselves. If you buy through our links we may earn a commission — it never changes a pick. How we choose
No power bank on this page was handled or tested. The charge counts below are arithmetic from published capacities, checked against Anker’s own published figures and against what owners report. Five of the 6 picks were in the top 10 of Amazon’s portable power bank Best Sellers list on 16 September 2026, when Amazon’s deals page was already marking early Prime Big Deal Days offers. The ranking is highest rating first, then most ratings.
The quick list
Every pick, in order. Jump to the full test on any of them.
- Highest rated here
CUKTECH 45W Power Bank, 20,000mAh, Built-in USB-C Cable
4.6 across 3,693 ratings, the top rating on this page, on a 20,000mAh unit owners describe as too heavy for a purse.
4.6from 3,693 verified reviews - Most-reviewed
Miady 2-Pack Portable Charger, Slim 10,000mAh
4.5 across 98,452 ratings, 2 slim 10,000mAh packs, and the widest split on quality and charging speed on this page.
4.5from 98,452 verified reviews - The one-phone travel day
Anker Zolo Power Bank, 10,000mAh 30W, Built-in USB-C Cable
4.5 across 14,960 ratings, and Anker publishes a charge count per phone, which makes it the clearest worked example of the maths.
4.5from 14,960 verified reviews - 20,000mAh from a deep sample
Anker Power Bank, 20,000mAh, Built-in USB-C Cable, 87W
4.5 across 9,809 ratings, with owners describing fast charging on long flights and road trips.
4.5from 9,809 verified reviews - Top of Amazon's power bank Best Sellers
INIU 10,000mAh 45W Fast Charging Portable Charger
4.4 across 86,559 ratings, and #1 on Amazon's portable power bank Best Sellers list when read on 16 September 2026.
4.4from 86,559 verified reviews - The laptop option, under 100 Wh
Anker Laptop Power Bank, 25,000mAh, 165W Total Output
4.4 across 12,004 ratings on a 25,000mAh unit that works out at 92.5 Wh, below the usual 100 Wh cabin limit.
4.4from 12,004 verified reviews
A power bank’s mAh is counted at 3.7 volts, not 5
The mAh on a power bank describes the lithium cells inside it at their nominal 3.7 volts. A phone battery is rated at its own cell voltage, commonly around 3.85 volts, and the energy travels between them over USB at 5 volts or more. Dividing one mAh figure by the other skips both the voltage difference and the losses in between.
Watt-hours fix that. Multiply mAh by 3.7 and divide by 1,000: a 10,000mAh bank holds 37 Wh, a 20,000mAh bank holds 74 Wh, and a 25,000mAh bank holds 92.5 Wh. Samsung lists the Galaxy S24 battery at 4,000mAh, which is about 15.4 Wh at a typical 3.85 volts.
About 80% of the stored energy reaches the phone
Every power bank loses energy raising 3.7 volts to USB voltage, and more is lost as heat in the phone’s own charging circuit. Battery publications and manufacturers put real-world efficiency at roughly 70% to 85%.
Anker’s own numbers show the loss. It says its 10,000mAh Zolo 30W delivers 1.94 charges to a Galaxy S24. That is about 30 Wh reaching the phone from 37 Wh stored, or roughly 80%. A simple rule follows: multiply the power bank’s mAh by 0.75, then divide by the phone’s mAh.
Even Anker’s own listing shows how loose these counts are. For the iPhone 14 Pro, one line of the listing says 2 charges and the specification table says 2.94. A charge count on a box is an estimate, and a phone that is in use while it charges will get fewer.
10,000mAh covers one phone through a long travel day
The rule gives about 1.9 charges from 10,000mAh for a 4,000mAh phone, and about 1.5 for a 5,000mAh phone. Anker lists 1.2 charges for the Pixel 9 Pro XL, a phone with a larger battery. For one phone across a day of airports, that is a full recharge with some left over.
TSA screening counts have put the Sunday after Thanksgiving at the top of the holiday travel period every year since 2021, and in 2026 that Sunday falls on 29 November. Long security lines and delayed connections are exactly when a 10,000mAh bank earns its place.
Anker Zolo Power Bank, 10,000mAh 30W, Built-in USB-C Cable
4.5 across 14,960 ratings, and Anker publishes a charge count per phone, which makes it the clearest worked example of the maths.
Current price shown on Amazon. We may earn a commission.
| Capacity | 10,000mAh (37 Wh) |
|---|---|
| Output | 30W |
| Size | 4.32 × 2.58 × 0.98 in |
4.5 across 14,960 ratings, and it sat in the top 5 of Amazon’s power bank Best Sellers list on 16 September 2026. Anker publishes a charge count for each phone: 2 for the iPhone 15, 1.94 for the Galaxy S24 and 10 for AirPods Pro 2.
Owners praise the deck-of-cards size and the built-in USB-C cable. Battery life and durability reports are mixed, and the full evidence profile of this Anker sets out where they divide.
Buy it if
- One phone and a pair of earbuds
- You want a cable you cannot forget
Don't buy it if
- You also need to charge a laptop
INIU 10,000mAh 45W Fast Charging Portable Charger
4.4 across 86,559 ratings, and #1 on Amazon's portable power bank Best Sellers list when read on 16 September 2026.
Current price shown on Amazon. We may earn a commission.
| Capacity | 10,000mAh (37 Wh) |
|---|---|
| Output | 45W |
| Watch | Battery life reports are mixed |
86,559 ratings at 4.4 and the #1 spot on Amazon’s power bank Best Sellers list when read on 16 September 2026. Owners like the 45W speed, the small size and the built-in cable.
Battery life is where reports split, with some owners describing a long-lasting charge and others finding it runs out sooner than expected. It ranks fifth here only because the house rule puts rating ahead of sample size.
Buy it if
- You want 45W speed in a 10,000mAh size
- A large, recent sample of owners
Don't buy it if
- You need 2 full phone charges without fail
Miady 2-Pack Portable Charger, Slim 10,000mAh
4.5 across 98,452 ratings, 2 slim 10,000mAh packs, and the widest split on quality and charging speed on this page.
Current price shown on Amazon. We may earn a commission.
| Capacity | 2 × 10,000mAh (37 Wh each) |
|---|---|
| Evidence | 98,452 ratings |
| Watch | Mixed speed and quality reports |
98,452 ratings at 4.5 is the deepest evidence base on this page, for 2 slim 10,000mAh packs sold together. Owners say each pack charges a phone more than once and call it a lifesaver while travelling.
Quality, speed and battery life are all mixed in the reports. Some owners describe fast, reliable packs and others describe slow charging and short life. Two travellers sharing the pair get 37 Wh each.
Buy it if
- Two travellers who each want their own pack
- Charge count matters more than charge speed
Don't buy it if
- You need a fast top-up between connections
20,000mAh is for 2 phones or 2 days
The same rule gives about 3.8 charges from 20,000mAh for a 4,000mAh phone. That covers 2 travellers sharing one bank for a day, or one traveller for 2 days without a wall socket.
The cost is weight and size. Owners of 20,000mAh units often describe them fitting a backpack but not a pocket or small bag, which matters on a day spent standing in queues. A bank that size belongs in the carry-on’s outer pocket, and how packing cubes and compression change carry-on space covers the rest of that bag.
CUKTECH 45W Power Bank, 20,000mAh, Built-in USB-C Cable
4.6 across 3,693 ratings, the top rating on this page, on a 20,000mAh unit owners describe as too heavy for a purse.
Current price shown on Amazon. We may earn a commission.
| Capacity | 20,000mAh (74 Wh) |
|---|---|
| Output | 45W |
| Watch | Size and weight |
4.6 across 3,693 ratings puts the CUKTECH first by the house rule, on under a quarter of the evidence behind the Anker 20,000mAh below. One owner describes up to 4 phone charges, which is close to what the arithmetic predicts.
Size is the dispute: some owners call it compact for its capacity, and others find it too big for a purse. Weight is the most common complaint.
Buy it if
- Two phones, or one phone for two days
- You want the highest rating over the deepest sample
Don't buy it if
- You carry it in a pocket or small bag
Anker Power Bank, 20,000mAh, Built-in USB-C Cable, 87W
4.5 across 9,809 ratings, with owners describing fast charging on long flights and road trips.
Current price shown on Amazon. We may earn a commission.
| Capacity | 20,000mAh (74 Wh) |
|---|---|
| Output | 87W max, 3 ports |
| Suits | Long flights, 2 devices |
4.5 across 9,809 ratings, and it was in the top 10 of Amazon’s power bank Best Sellers list on 16 September 2026. Owners describe quick charging and use it on long flights and road trips.
The built-in USB-C cable comes up repeatedly as a reason to choose it. At 74 Wh it sits well inside the cabin limit.
Buy it if
- A phone and a tablet on the same trip
- You want Anker's larger unit with a built-in cable
Don't buy it if
- Weight matters more than capacity
Watts decide how fast, not how many
A 30W and a 45W power bank of the same 10,000mAh hold the same 37 Wh. The higher wattage refills a phone faster, but it does not add a charge.
Anker says its 30W Zolo takes an iPhone 16 Pro Max to 50% in 27 minutes. That is the figure that matters during a 40-minute layover, and it only applies if the phone supports that speed. Recharging the bank matters too: the Zolo takes 20W input, so the bank itself needs hours on a wall charger rather than minutes.
25,000mAh sits just below the 100 Wh cabin limit
Airline and security rules commonly allow spare lithium batteries up to 100 Wh in the cabin without airline approval, and spare batteries never go in checked bags. A 25,000mAh bank at 3.7 volts is 92.5 Wh, just under that line. A 28,000mAh bank, at 103.6 Wh, would not.
The full carry-on rules for liquids and lithium batteries cover the 100 to 160 Wh band, which needs airline approval. Many power banks print Wh on the case, and security staff read that figure rather than mAh.
Anker Laptop Power Bank, 25,000mAh, 165W Total Output
4.4 across 12,004 ratings on a 25,000mAh unit that works out at 92.5 Wh, below the usual 100 Wh cabin limit.
Current price shown on Amazon. We may earn a commission.
| Capacity | 25,000mAh (92.5 Wh) |
|---|---|
| Output | 165W total |
| Watch | Some early failures reported |
4.4 across 12,004 ratings, and in the top 10 of Amazon’s power bank Best Sellers list on 16 September 2026. At 92.5 Wh and 165W total output, it is the one pick here built to charge a laptop alongside a phone and a tablet.
Owners praise its capacity and built-in USB-C cables for extended trips. Some report it failing within 2 months, and several say it is heavy.
Buy it if
- A laptop, a phone and a tablet on one trip
- You want to stay under 100 Wh
Don't buy it if
- You only charge a phone
What mAh on the box cannot tell you
A capacity figure says nothing about cell quality, and cell quality decides both the real efficiency and how fast capacity fades. Supplier buying guides put lower-grade cells at 60% to 75% efficiency, against 85% or more for better ones, and nothing on a listing tells the two apart.
Owner reports are the only check available without a meter. The mixed battery-life reports on several picks above are the practical sign of that variation, and a bank that delivered 2 charges when new may deliver fewer after a year of use.