A 10,000 mAh power bank can run a 5-watt load for about 12–18 hours; higher wattage drains it sooner.
Planning a trip or a long workday and wondering how many hours your backup battery will keep your gear alive? Run time depends on three things: stored energy, the power your device draws, and losses during conversion.
Power Bank Run Time After A Full Charge: What To Expect
Energy in these packs is labeled in milliamp-hours at the cell’s native voltage (usually 3.6–3.7 V). Devices sip power at 5 V or higher, so a boost converter steps voltage up and wastes some energy as heat. Real-world efficiency often lands around 60–75% depending on load and cable quality. That’s why the usable output of a 10,000 mAh pack is closer to 6,000–7,500 mAh at 5 V.
Quick Capacity-To-Hours Estimates
Use the table below to turn capacity into hours for common loads.
| Pack Size (mAh) | Usable Energy (Wh)* | Hours At Load |
|---|---|---|
| 5,000 | 11–14 | 5 W: 6–9 | 10 W: 3–4 | 20 W: 1–1.5 |
| 10,000 | 22–28 | 5 W: 12–18 | 10 W: 6–9 | 20 W: 3–4 |
| 20,000 | 44–56 | 5 W: 24–36 | 10 W: 12–18 | 20 W: 6–9 |
| 27,000** | 60–75 | 5 W: 30–45 | 10 W: 15–22 | 20 W: 7–11 |
*Usable Wh assumes 60–75% conversion efficiency from 3.7 V cells to USB output. **Around many airlines’ 100 Wh cap.
What Those Numbers Mean Day-To-Day
A phone pulling 5–8 W during maps and music lands in the mid rows above. A compact laptop on USB-C can ask for 20–45 W; the largest packs keep that going for long.
How To Do A Fast Back-Of-Napkin Calculation
- Convert mAh to Wh. Multiply the printed mAh by 3.7 V, then divide by 1000. A 10,000 mAh unit holds about 37 Wh at the cells.
- Apply efficiency. Multiply by 0.6–0.75 to account for boost conversion and cable losses. That 37 Wh becomes 22–28 Wh at the port.
- Divide by your load. Hours ≈ usable Wh ÷ device watts. At a 10 W draw, you’ll see about 2.2–2.8 hours for each 22–28 Wh segment; scale from there.
If your device shows current in amps, another route is: hours ≈ (mAh × 0.6–0.75) ÷ mA, assuming a 5 V output.
What Shrinks Or Stretches Run Time
Output Power Setting
USB-C ports that speak USB Power Delivery can raise voltage to 9 V, 12 V, 15 V, or higher to match fast-charge profiles. Higher voltages help the phone charge fast, but the wattage surge drains the pack faster in hours. Total energy stays the same; you just spend it quicker.
Screen Time And Radio Use
Brightness, video recording, navigation, and 5G all push draw upward. If you watch offline video at low brightness, your draw can drop to 3–5 W and your hours rise.
Cable And Accessory Losses
Long, thin cables waste energy. Short, good-gauge USB-C cables reduce voltage drop. Wireless pads add extra loss, cutting delivered energy.
Temperature
Cold reduces chemical activity inside lithium cells and lowers output; heat accelerates aging. Keep the pack shaded and off dashboards.
Age And Cycle Wear
All lithium cells lose capacity over cycles. Partial charges are fine and even gentle. Deep drains speed wear. A one-year-old pack may still be near peak; a heavy-use pack after hundreds of cycles will run for fewer hours than when new.
Standby After Charging: How Long Until It Self-Drains?
Even when idle, lithium cells slowly lose charge. Expect a small drop in the first day after a full top-off, then a slow trickle each month. Protection circuits inside the pack also draw a little. A topped pack stored in a drawer will still have usable charge weeks later, but not the same level you left it with. Research on self-discharge notes a small early drop, then about 1–2% per month plus a little draw from the protection circuit.
Fast-Charge Myths And Realities
Fast-charge logos don’t change the energy inside the pack. They change the rate at which energy moves. A 20,000 mAh unit that supports 30 W output can refill a phone fast, yet it will still run a 10 W device for around the same 12–18 hours shown earlier. Rate affects time to fill the phone, not total hours available.
Device Examples In Plain Numbers
A compact phone streaming music with the screen off hovers near 3–4 W. On a 10,000 mAh pack that means 6–9 hours of play time. A big phone shooting video can sit near 10–12 W, which trims that to about 2–3 hours of direct power.
A mid-size tablet playing downloaded video at medium brightness often lands in the 10–15 W band. With 22–28 Wh usable from a 10,000 mAh unit, you’re looking at 1.5–2.5 hours before the pack empties. A 20,000 mAh pack doubles that window.
Thin laptops idle near 10–15 W but spike above 30 W under load. Near-100 Wh packs offer breathing room; plan for short top-ups, not full work sessions.
Sizing Guide For Real-World Uses
Pick your use case, find the typical draw, then match a pack size to reach your target hours. These ranges reflect common gear and tasks.
| Use Case | Typical Draw | Suggested Pack |
|---|---|---|
| All-day phone navigation + music | 6–10 W | 10,000–20,000 mAh |
| Tablet video on flights | 10–15 W | 20,000 mAh |
| Handheld console gaming | 15–20 W | 20,000–27,000 mAh |
| Ultrabook trickle on USB-C | 20–30 W | 27,000 mAh (near 100 Wh) |
| Action camera + phone top-ups | 3–8 W | 10,000 mAh |
Why Your Pack’s Label Doesn’t Match Real Output
The printed capacity describes energy at the internal cell voltage. After voltage boost and conversion losses, the rated output feels smaller. Many makers print a second “rated capacity” on the spec sheet that reflects this. If you see two numbers (like 10,000 mAh and 6,068 mAh), the lower one is the expected output at 5 V under standard tests.
Quick Math With Device Batteries
Think in refills: match your phone’s battery size to the pack’s rated output. A 5,000 mAh phone and a pack that can deliver 6,000–7,500 mAh should yield one full refill plus a top-up, accounting for overhead.
Care Tips That Preserve Hours
Charge In Gentle Ranges
Keep day-to-day levels between 20% and 80%. Full charges before travel are fine; try not to leave the pack baking at 100% in heat.
Use Reliable Cables And Chargers
Match the charger’s wattage to the pack’s input rating. If the pack supports 18–30 W USB-C input, use a PD charger so refills are quick and efficient.
Store Smart
For long storage, set the level mid-pack and keep it cool. Press the status button monthly; top off if it fell below the midpoint.
How We Built These Ranges
The ranges use common device draws, standard mAh-to-Wh conversion at 3.7 V, and typical conversion loss. We cross-checked with maker specs that list both capacity and rated output, plus research on lithium self-drain and pack electronics. We also checked airline watt-hour limits so the sizing tips match travel rules for passenger carry-on batteries worldwide today.
Takeaways You Can Act On
- Multiply mAh by 3.7 and by 0.6–0.75 to get usable Wh.
- Divide usable Wh by your device’s watts to get hours.
- Higher output watts shorten hours; energy stays the same.
- Top off the pack before trips; idle cells slowly self-drain.
- Buy the size that fits your wattage, not just your mAh wish.