A 10,000 mAh power bank typically delivers about 6,500–7,500 mAh to devices, which equals roughly 1–2 full phone charges.
Here’s the short version in plain math. A 10,000 mAh pack stores energy in 3.7 V cells. When it boosts that to USB output, some energy turns to heat. Most well-made units land near 70–90% conversion on a good cable and a healthy temperature range. That leaves about 6,500–7,500 mAh to hand off at 5 V. Bigger phones with 4,500–5,000 mAh batteries get about one full charge plus a bit. Smaller phones in the 3,000–3,500 mAh range can get two full top-ups in friendly conditions.
Charging Capacity Of A 10000 mAh Power Bank: Quick Math
The clean way to reason about this is in watt-hours (Wh):
- Stored energy: 10,000 mAh × 3.7 V ≈ 37 Wh.
- Usable energy at USB output: 37 Wh × efficiency (often 0.7–0.9) ≈ 26–33 Wh.
- Convert back to “5 V mAh” for intuition: 26–33 Wh ÷ 5 V ≈ 5,200–6,600 mAh delivered at 5 V.
Some makers present this step directly. See Anker’s explanation of 3.7 V cell ratings and 5 V output math. A recent Anker capacity guide also pegs conversion loss near 10–30% in normal use.
What That Means For Real Devices
Phone batteries span a wide range. Many iPhones sit near 3,000–4,400 mAh depending on model year, while many Android flagships sit near 4,500–5,500 mAh. For context on recent Apple sizes, see this rolling list of iPhone battery capacities in mAh and Wh. With that frame, a 10,000 mAh bank gives one strong top-up for big batteries or two tidy refills for smaller ones.
Quick Reference Table: Typical Outcomes
The table below uses a midrange 75% conversion and friendly conditions (room temperature, decent cable, device not in heavy use while charging).
| Device Battery Size | Estimated Full Charges | Notes |
|---|---|---|
| 3,000 mAh phone | ~2.2× | Room for screen-on use during charging. |
| 3,500 mAh phone | ~1.9× | Two fills if the phone is near idle. |
| 4,000 mAh phone | ~1.6× | One full, plus a healthy top-off. |
| 4,500 mAh phone | ~1.4× | One full, plus ~40% extra. |
| 5,000 mAh phone | ~1.3× | One full, plus ~30% extra. |
| 5,500 mAh phone | ~1.2× | One full, plus a small buffer. |
| Small tablet ~7,500 mAh | ~0.9× | Almost one complete refill. |
How The Numbers Are Built
The 3.7 V Cell And 5 V USB Output
Inside the case are one or more lithium-ion cells near 3.7 V nominal. USB-A and USB-C ports serve closer to 5 V during standard charging or negotiate higher voltages for fast-charge modes. Stepping 3.7 V up to the output level isn’t free. Some energy turns to heat in the converter. That’s the main reason your 10,000 mAh sticker doesn’t translate one-for-one into phone refills.
Conversion Losses You’ll Actually Notice
- Electronics overhead: The boost converter and the battery’s internal resistance eat a slice of the pie.
- Heat: Charging while gaming or in a hot car wastes more energy and trims the final tally.
- Voltage steps during fast charge: Higher-voltage modes (9 V, 12 V, 20 V) reduce cable current but still carry conversion loss in the bank and in the phone.
- Cable quality: Thin or long cables raise resistance. A short, well-made cable preserves more of the stored energy.
Sample Scenarios You Can Trust
Small Battery Phone (~3,200–3,500 mAh)
On a day trip, you can refill twice if the phone is idle while charging. If you watch video or shoot photos while it charges, expect closer to 1.7–1.9 rounds. That gap comes from the device drawing power at the same time you’re trying to refill it.
Large Battery Phone (~4,800–5,500 mAh)
You’ll get one dependable refill and a bonus top-off. With a 5,000 mAh handset, a 10,000 mAh bank at ~75% conversion gives around 7,500 mAh at 5 V, which is one full charge and ~50% more if the phone is idle during the second session. Real use often lands near 30–40% extra because screens stay on and radios stay busy.
Small Tablet Or E-Reader (6,000–8,000 mAh)
Expect almost a full refill on compact tablets or several e-reader refills. Readers tend to sip power, so the same bank feels generous here.
Make Your 10,000 mAh Bank Go Farther
Charge Habits That Save Energy
- Top off earlier: Starting at 20–40% state of charge avoids long runs near the knee of the curve where heat and resistance climb.
- Let the phone rest while charging: Screen off, GPS off, camera closed. Less parallel draw means more energy lands in the battery.
- Use a short, good cable: Keep runs tidy. Poor cables waste energy and slow the session.
- Keep things cool: Shade and airflow help both the bank and the phone.
- Match ports to needs: If your bank and phone both support USB-C PD, use that port and a C-to-C cable for steady, efficient sessions.
Know When To Step Up In Size
Weekend trips, heavy video capture, or hotspot duty add load that a 10,000 mAh unit may not cover twice over. If your phone sits near 5,000–6,000 mAh and you plan two long refills between wall charges, a 20,000–26,800 mAh pack fits better. The math is identical; you’re just starting with ~74–99 Wh of stored energy instead of 37 Wh.
Reality Check: Why Estimates Differ
No two sessions are alike. A vendor’s rated capacity uses controlled conditions. Your day is messy: location changes, temperature swings, screen time, and background tasks. Expect spread in your results and use the ranges here to plan with a buffer. If your bank is a few years old, baked-in wear trims capacity further, so target the low end of the range.
Worked Examples With Numbers
Case A: 4,000 mAh Phone With 75% Conversion
Stored energy is 37 Wh. Usable is ~27.75 Wh. At 5 V, that’s ~5,550 mAh. Divide by a 4,000 mAh battery and you get ~1.39 full charges. In the real world you’ll see about 1.3–1.4, depending on screen time.
Case B: 5,000 mAh Phone With 80% Conversion
Usable is 37 Wh × 0.80 = 29.6 Wh. At 5 V, that’s ~5,920 mAh. Divide by 5,000 mAh and you get ~1.18 full charges. With the phone idle, you may push to ~1.2–1.3.
Case C: 3,300 mAh Phone With 70% Conversion
Usable is 25.9 Wh, or ~5,180 mAh at 5 V. Divide by 3,300 and you get ~1.57 full charges. If you run maps or video during the session, expect closer to ~1.4–1.5.
Why Watt-Hours Beat mAh For Planning
mAh makes sense only at a stated voltage. Phone batteries and power banks publish different voltages, so matching in Wh avoids confusion. A 10,000 mAh bank at 3.7 V holds 37 Wh, which is the apples-to-apples number you can compare to another pack or to a device that lists its battery in Wh. Airlines also use the Wh rating on portable chargers for allowance checks, which lines up with this approach.
Table: Usable Energy And Charge Counts By Efficiency
Pick your best guess for conditions and read across.
| Efficiency | Usable At 5 V | Full Charges For 4,000 mAh Phone |
|---|---|---|
| 70% | ~5,180 mAh | ~1.30× |
| 75% | ~5,550 mAh | ~1.39× |
| 80% | ~5,920 mAh | ~1.48× |
| 85% | ~6,290 mAh | ~1.57× |
| 90% | ~6,660 mAh | ~1.66× |
Common Questions, Answered Inline
Does Fast Charging Change The Total Number Of Refills?
Not much. Fast modes shift voltage and current to speed up the session, but the energy bucket stays the same. You may see slightly fewer refills if heat rises or if the bank spends more time in conversion overhead.
Why Does My Bank Feel “Smaller” In Winter Or In A Hot Car?
Cold raises internal resistance and drops voltage sooner, while heat drives more loss in the converter and battery. Keep both the pack and the phone near room temperature for the best return.
Why Is The Label In mAh But My Airline Asks For Wh?
mAh is common in retail packaging. Airlines care about total energy. Convert with Wh = (mAh × cell voltage) ÷ 1000. For a 10,000 mAh unit with 3.7 V cells, that’s ~37 Wh.
Checklist: Get The Most From 10,000 mAh
- Leave with the bank at 100% and a short, good cable in the bag.
- Start charging when your phone dips to 30–40%.
- Set the phone down while it charges; screen off saves energy.
- Keep both devices out of direct sun or freezing air.
- If you need two large refills before a wall stop, step up to 20,000 mAh or more.
Rule-Of-Thumb Recap You Can Rely On
A 10,000 mAh bank equals roughly 37 Wh on the inside and hands off about 26–33 Wh to your devices in normal use. In plain terms, that’s one full refill for big-battery phones with a little extra, or two refills for compact phones when you charge with the screen off. If your days run long and heavy on camera or hotspot duty, a larger pack fits the job better. If not, this size still hits a sweet spot for weight, price, and everyday carry.