A 10,000 mAh power bank usually gives 1–2 full phone charges (about 26–31 Wh usable), depending on device size and efficiency.
If you picked up a 10k mAh portable charger and want to know what you’ll get out of it, the quick math points to “enough for a day or two of phone use.” The finer answer depends on three things: usable energy after conversion losses, the battery size of the device you’re charging, and how fast you push power in or out. This guide shows the numbers, clear scenarios, and simple rules so you can predict run time without guesswork.
How Long Will A 10,000 mAh Charger Run? Practical Answer
Inside these packs sits a lithium-ion cell (or a few cells) with a nominal voltage near 3.7 V. Advertised capacity (10,000 mAh) refers to that cell voltage. USB ports deliver 5 V or a negotiated USB-C PD voltage, so the pack boosts voltage up and your phone steps it down again. Each stage wastes a slice as heat. That’s why usable energy is lower than the label.
Quick Formula You Can Use
Usable Wh ≈ (mAh ÷ 1000 × 3.7) × efficiency. A 10,000 mAh unit stores about 37 Wh at the cell. With real-world efficiency between 70–85%, you’ll see roughly 26–31 Wh delivered to the device battery.
Table: Typical Charges From A 10k Pack
This table uses common device battery sizes in watt-hours and assumes 70–85% overall efficiency. Treat the “charges” column as full 0–100% cycles; topping up from 20–80% counts as a partial cycle.
| Device Type | Battery (Wh) | Estimated Full Charges |
|---|---|---|
| Compact Phone | 11–13 | 2.0–2.6 |
| Large Phone | 16–19 | 1.4–1.9 |
| Small Tablet | 19–28 | 0.9–1.6 |
| Wireless Earbuds Case | 1–2 | 13–31 |
| Action Camera | 5–7 | 3.7–6.2 |
| Smartwatch | 0.5–1 | 26–62 |
Where The Numbers Come From
Watt-Hours Beat Milliamp-Hours
Energy math works best in watt-hours. Aviation regulators publish a simple rule: Wh = Ah × V (or mAh ÷ 1000 × V). That’s the clean way to convert a label like “10,000 mAh at 3.7 V” into energy you can compare across devices. See the official guidance on the FAA watt-hour formula.
Efficiency Eats A Chunk
Energy leaves the pack through a boost converter, travels through a cable, then drops again inside the phone’s charging circuit. Lab data on lithium-ion shows energy efficiency can range across the mid-70s to upper-90s depending on rate and heat. Battery University summarizes how energy efficiency shifts with charge and discharge rates; planning with a 70–85% window lines up well with field results (coulombic and energy efficiency).
Real-World Math
Say your phone has a 16 Wh battery. A 10k pack with 31 Wh usable at the high end gives about 31 ÷ 16 ≈ 1.9 full charges. With 26 Wh usable, it’s 1.6. Match your device size to the first table for a fast estimate.
Close Variation: How Long Will A 10000 mAh Power Bank Power A Phone? Methods That Work
Use three quick checks to predict runtime with confidence. First, convert the pack label to watt-hours. Second, apply a sensible efficiency range. Third, divide by your device’s battery size.
Step 1: Convert The Label
Raw energy of a 10k pack: 10,000 mAh ÷ 1000 × 3.7 V ≈ 37 Wh. This aligns with battery standards that describe nominal cell voltage near 3.7 V for common chemistries.
Step 2: Apply Efficiency
Pick 0.70 for hard use, 0.80 as a middle case, and 0.85 for gentle, cool charging. Usable energy spans 26–31 Wh in most cases. Expect values near the lower end when fast-charging in warm conditions or using long, thin cables.
Step 3: Divide By Device Battery Size
Common phone batteries sit near 11–19 Wh. Small phones land about 2–3 full cycles; big flagships land around 1.5–2 cycles. Tablets are larger, so you may see a single full cycle with some headroom for earbuds or a watch.
What Changes The Outcome
Charge Rate (W)
High wattage shortens time but trims efficiency. Fast USB-C PD profiles run hotter, which wastes a bit more energy. If you want the longest total run time from the same pack, slower charging often wins by a small margin.
Cable And Port Losses
Thin, long, or damaged cables raise resistance and drop voltage. The pack works harder to hold the target voltage, which wastes power. Short, certified cables help maintain efficiency and reduce heat.
Heat
Warm batteries lose more energy as heat during charge and discharge. Keep the pack out of direct sun, give it airflow while fast-charging, and avoid covering it under bedding or in a pocket while pushing high wattage.
Device Behavior
Phones sip power for the screen, radios, and background tasks while charging. If you game or record video during a top-up, some of the pack’s output runs the phone instead of filling the battery, which stretches charge time and lowers the final delivered energy.
Second Table: Recharge Time For The Pack Itself
The figures below estimate how long it takes to refill a 10k pack from empty. They assume about 37 Wh stored and typical overhead.
| Charger Input (W) | Approx. Time To Refill | Notes |
|---|---|---|
| 5 W (old USB) | 8–9 hours | Longest time; fine for overnight |
| 10 W | 4–5 hours | Common wall bricks |
| 18–20 W USB-C PD | 2.5–3 hours | Many modern packs support this |
| 30 W USB-C PD | ~2 hours | Only if the pack accepts it |
Quick Device-Specific Estimates
Phones
Small phones with 11–13 Wh batteries: expect two full charges plus a bit. Big phones with 16–19 Wh batteries: plan on around one and a half to nearly two. If the phone supports very high PD rates, you might trade a little efficiency for speed, yet total cycles stay in the same band.
Tablets
Small tablets often carry 19–28 Wh batteries. A 10k pack will top one up once with a cushion for earbuds or a watch. Large tablets need a bigger pack for multiple full cycles.
Wearables And Accessories
Earbud cases, action cameras, GPS bike computers, and watches draw tiny amounts. A single 10k unit can recharge them many times. It’s handy to pair a short cable so the pack isn’t working against voltage drop.
How To Stretch Every Watt-Hour
Keep It Cool
Store and charge at room temperature. Avoid hot cars and sunny windowsills. Heat hurts efficiency and long-term capacity.
Match The Cable
Use certified, short cables rated for the wattage you need. Replace frayed or loose cables that cause dropouts or heat.
Charge Smart
If you’re camping or traveling, a slower top-up can squeeze more total energy into the phone. Save the fastest PD mode for quick boosts when time matters more than raw efficiency.
Avoid Deep Storage Discharge
Letting a pack sit empty for months accelerates aging. Park it around 40–60% if you won’t use it for a while, and give it a brief recharge every few months.
Simple Calculator You Can Do In Your Head
1) Convert the pack label to Wh: divide mAh by 1000 and multiply by 3.7. 2) Multiply by 0.7–0.85 for real-world usable energy. 3) Divide by your device’s Wh. That ratio is your rough count of full charges.
Why Specs Don’t Always Match Your Results
Capacity Labels Use Cell Voltage
Manufacturers report capacity at the internal cell voltage, not the USB output voltage. That’s standard practice across portable batteries and explains why a label can’t be compared directly to a device running at a different voltage.
Fast Modes Raise Heat
High PD profiles are great for speed, but extra heat trims delivered energy. If your goal is the most charges per pack, use a mid-range power profile and let the device rest while it fills.
Background Drain Adds Up
Streaming, maps, hotspot use, and camera work during charging can double the time to fill and shave a few percent off the total energy that reaches the battery.
Sources Behind The Math
The FAA watt-hour formula explains the Wh = Ah × V conversion used across consumer batteries. Battery University publishes measurements showing energy efficiency varies with rate and temperature; that supports the 70–85% planning range used in this guide (coulombic and energy efficiency).
Bottom Line For A 10k Pack
Expect one and a half to two full phone charges in normal use, more with smaller phones, and about one small-tablet refill. Keep the pack cool, use a solid cable, and pick charging speeds to suit your goal: fastest top-ups or the most total energy.