A 10,000mAh power bank refills about 1.4–1.8 full phone charges, depending on usable energy, phone size, and charging losses.
Shoppers see “10,000mAh” on the box and expect two or three full refills. Real-world results sit closer to one-and-a-half. The gap comes from how power banks are rated, conversion from their cell voltage to USB output, and day-to-day inefficiencies. This guide gives you the math up front, then shows the levers that move your result.
How Many Phones A 10,000mAh Power Bank Can Refill
Inside most packs, the cells sit near 3.7–3.85V. The label counts capacity at that internal voltage. USB ports send 5V or higher. During step-up, some energy turns into heat. That means the usable energy you can pass to a phone is lower than the printed figure.
From mAh To Wh, Then Back Again
Energy math runs on watt-hours (Wh): mAh ÷ 1000 × volts. A 10,000mAh pack at 3.7V holds about 37Wh of energy. Brand spec sheets often confirm this, and some even list a lower “rated capacity” at 5V that reflects conversion losses. One common model lists 37Wh total and rated capacity 5,500mAh at 5V/3A, which equals 27.5Wh at the port.
Phone Sizes And Estimated Refills (Table)
The table below uses a usable energy slice of 27.5Wh (a common rated figure for 10,000mAh units) and assumes screen off while charging.
| Phone Battery Size | Estimated Full Refills | Notes |
|---|---|---|
| 3,000mAh (≈11.6Wh) | ~2.3× | Small phones and older models |
| 4,000mAh (≈15.4Wh) | ~1.8× | Mid-range sweet spot |
| 4,500mAh (≈17.3Wh) | ~1.6× | Many mainstream Android phones |
| 5,000mAh (≈19.3Wh) | ~1.4× | Large phones and gaming models |
| 5,500mAh (≈21.2Wh) | ~1.3× | Battery-focused models |
Why Printed mAh Rarely Matches Your Result
Three factors shape your outcome: internal-to-USB conversion, cable and connector losses, and how the phone draws power during fast charge modes. A spec page from the USB standards group explains how USB Power Delivery raises voltage to deliver higher wattage at the same or lower current. Higher voltage cuts cable loss, but every conversion stage still shaves a bit of energy.
Internal Voltage Vs USB Output
Cells inside the bank sit around 3.7V. The step-up converter raises that to 5V or PD levels. Brand documentation and lab tests often show real-world efficiency between about 70% and 85% from cell to port, which lines up with the “rated capacity at 5V” many vendors print on spec sheets.
Fast Charge Modes
PD and proprietary turbo modes push higher power for a short window, then taper. Peaks shorten charge time, but a hot converter and phone draw add loss. The end number of refills usually drops a little compared to a slow 5V/2A session.
Screen, Radios, And Background Use
If you scroll, game, or tether while charging, the phone spends some of the incoming energy straight away. The pack needs extra watt-hours to reach 100%, which trims the count of full refills.
How To Estimate Your Own Refills
You can predict your result in two quick steps without tools.
Step 1: Find The Bank’s Usable Energy
Check the fine print on the shell or spec page. Many 10,000mAh units list energy as 37Wh and a rated number at 5V around 5,000–6,000mAh. If you only see 10,000mAh, convert: 10,000 ÷ 1000 × 3.7 ≈ 37Wh. Then multiply by an efficiency guess (0.7–0.85) to get usable Wh. Some brands publish both numbers, which saves you the guesswork.
Step 2: Convert Your Phone Size To Wh
Multiply your phone mAh by 3.85V and divide by 1000. A 4,500mAh phone lands near 17.3Wh. Then divide the bank’s usable Wh by that number. That quotient is your estimated count of full refills. Round down one tenth to cover cable and idle drain.
Worked Examples With Realistic Settings
Here are three common matchups using a 10,000mAh bank with 27.5Wh usable at the port and a solid USB-C cable.
Small Phone (3,800mAh)
Phone energy: 3,800 × 3.85 ÷ 1000 ≈ 14.6Wh. Estimated refills: 27.5 ÷ 14.6 ≈ 1.88×. Expect near two fills if the screen stays off.
Mainstream Phone (4,500mAh)
Phone energy: 4,500 × 3.85 ÷ 1000 ≈ 17.3Wh. Estimated refills: 27.5 ÷ 17.3 ≈ 1.59×. Expect around one-and-a-half fills.
Large Battery Phone (5,500mAh)
Phone energy: 5,500 × 3.85 ÷ 1000 ≈ 21.2Wh. Estimated refills: 27.5 ÷ 21.2 ≈ 1.30×. Two full charges are unlikely unless you trickle at low current and avoid any use.
Efficiency Cliffs That Cut Your Count
Not all losses are equal. These common traps can drop the total by a large chunk.
Thin Or Long Cables
High resistance turns power into heat along the wire. Use a short, certified cable, ideally 60W-rated USB-C for PD. It runs cooler and wastes less, especially near the end of the charge where voltage negotiation changes.
Warm Gear
Converters and phone batteries lose efficiency when hot. Keep the bank and phone shaded and spaced during a fast top-off. A cool setup nets more delivered watt-hours over the same session.
Low State Of Charge Starts
Charging from 5% to 90% is an easy climb. The last 10% always slows and wastes a bit more. If you care about totals, stop around 90% and move on to the next refill.
Charging Modes And What They Mean
Ports and logos can be confusing. Here is a quick rundown and what they imply for refill counts.
| Port/Mode | What It Does | Impact On Refills |
|---|---|---|
| 5V USB-A (2A–2.4A) | Basic 10–12W output | Cool and efficient; near the estimates above |
| USB-C PD 9–12V | Higher voltage for faster top-ups | Quicker fills; a small hit to total count |
| Proprietary Turbo | Brand-specific high power bursts | Fast early phase; more heat, slightly fewer full refills |
Choosing A Bank If You Want More Refills
If your target is two full refills for a big phone, a 10,000mAh unit rarely gets there. Aim for 20,000mAh or look for a 10,000mAh unit with a published high “rated capacity at 5V.” Some brands list 6,000–6,500mAh at 5V for their premium models, which can squeeze a little more out of the same size shell.
Specs That Actually Matter
- Rated capacity at 5V: A direct view of usable energy. One Xiaomi sheet lists 5,500mAh at 5V on a 10,000mAh model, which maps to the math in this guide.
- Energy in Wh: A universal figure across devices. 37Wh is typical for this size and lines up with airline rules.
- PD voltage range: Wider support helps your phone hold peak power longer without cable heat.
Real-World Scenarios And Tips
Weekend Trip With Light Use
Carry one compact bank and a short USB-C cable. Top up at lunch and before bed. Keep your phone in airplane mode while sleeping. That pattern stretches the bank to two mid-size refills across the weekend.
Commuter With Daily Music And Maps
Plug in during the ride home rather than the morning dash. Charging later avoids battery drain from cold starts and cuts idle loss at your desk.
Mobile Hotspot Day
Tethering hammers the radio and CPU. Expect your refill count to fall by a third. If you must hotspot, run the bank at basic 5V instead of PD to keep heat down.
Troubleshooting Poor Results
The Bank Feels Hot And Refills Are Low
Swap the cable first. Then try a lower power mode. If the case still runs warm, the converter may be inefficient. A unit with a better rated capacity at 5V will likely deliver more energy in the same sessions.
The Phone Says “Charging Slowly”
Some phones require a PD handshake for full power. Use a USB-C to USB-C cable and a PD-labeled port. Watch for the charge icon change; if nothing changes, stay patient and you will still reach a full refill, just not fast.
The Bank Stops Near 20%
Many packs reserve a buffer to protect the cells from deep discharge. That reserve is normal and part of why you cannot drain the full printed mAh into your phone.
Why Watt-Hours Beat mAh For Shopping
mAh only makes sense when voltage matches. Power banks run at one voltage inside and another at the port, so mAh invites confusion. Watt-hours compare energy on equal terms. If two 10,000mAh banks list different Wh figures or different rated capacity at 5V, the one with the higher posted energy will refill more phones.
A Note On Airline Limits
Most airlines cap carry-on batteries at 100Wh. A 10,000mAh bank at 3.7V sits near 37Wh, well under that line. Larger units near 26,800mAh hover around 99Wh. That is why you often see that size marketed as the largest travel-friendly pack.
Method In Brief
This guide uses two public anchors: the USB standards page on USB Power Delivery for voltage behavior and a brand spec that lists both total energy and a lower 5V rated output: rated capacity 5,500mAh at 5V/3A. Those figures square with the math: 10,000mAh × 3.7V ≈ 37Wh total, and a rated 5,500mAh at 5V equals 27.5Wh at the port, which mirrors a cell-to-port efficiency near three quarters. PD raises voltage in steps on request, which helps cut cable loss but still carries small converter overhead.
Quick Back-Of-Envelope Calculator
Grab two numbers and you are set: bank Wh and phone mAh. If the bank only shows mAh, convert to Wh with mAh ÷ 1000 × 3.7. If your phone lists only mAh, turn it into Wh with mAh ÷ 1000 × 3.85. Then divide bank Wh (after efficiency) by phone Wh.
- Bank Wh: 10,000mAh → 37Wh; apply 0.75 for a safe estimate → ~27.8Wh.
- Phone Wh: 4,700mAh → ~18.1Wh.
- Refills: 27.8 ÷ 18.1 → ~1.5 full charges.
Bottom Line For Shoppers
A 10,000mAh portable bank delivers about 27–30Wh at the port in real use. That turns into around 1.4–1.8 refills for mid-size phones and 1.2–1.5 for bigger ones. Cable quality, heat, and charge mode slide the number up or down. If you need more headroom, pick a higher Wh unit or a model with a stronger rated output at 5V.