Power bank charge time depends on capacity, charger watts, and efficiency; many units take 2–6 hours, while fast USB-C models can drop under 90 minutes.
Here’s a clear way to predict charge time. With your bank’s milliamp-hours (mAh) and the watt rating of your charger and cable, you can forecast how long a refill takes and how well that bank tops up a phone, tablet, or laptop.
Power Bank Charging Time Guide
Portable packs store energy in watt-hours (Wh). Labels often show mAh, which maps to Wh using voltage. Most single-cell packs sit near 3.7 volts, so a handy estimate is: Wh ≈ (mAh ÷ 1000) × 3.7. Charging time then maps to energy divided by power: hours ≈ Wh ÷ charger watts ÷ efficiency. Real devices lose some energy to heat and conversion, so plan a buffer.
Quick Formula You Can Use
Time (hours) ≈ (Capacity in mAh ÷ 1000 × 3.7) ÷ Charger W × 0.85–0.95
Pick 0.90 for an everyday estimate. If the pack or cable runs warm, use 0.85. If both parts are strong USB-C gear, 0.93–0.95 can be realistic.
Typical Charge Times By Capacity
The table below gives ballpark times for common sizes with three charger powers. It assumes modern USB-C gear and about 90% overall efficiency.
| Capacity (mAh) | Charger Power | Time To Full |
|---|---|---|
| 5,000 | 18W USB-C | ~1.1–1.4 hours |
| 10,000 | 20W USB-C | ~1.9–2.3 hours |
| 20,000 | 30W USB-C | ~2.5–3.1 hours |
| 20,000 | 45W USB-C | ~1.7–2.1 hours |
| 27,000 (99Wh) | 65W USB-C | ~1.6–2.0 hours |
| 30,000 | 100W USB-C | ~1.2–1.6 hours |
What Sets The Pace
Four pieces shape the clock: capacity, the negotiated input power, the cable rating, and heat.
Capacity And Voltage
Portable packs use lithium-ion cells with a nominal voltage near 3.7V per cell. Larger bricks may stack cells for capacity or higher voltage with a step-down regulator. Marketing prints mAh at cell voltage, but charging happens at port voltage. Converting to Wh first gives an apples-to-apples number.
Charger Wattage And USB Power Profiles
USB-C with Power Delivery (PD) negotiates voltage and current. Older USB sat at 5V and low current. Modern PD steps to 9V, 15V, 20V, and, with Extended Power Range, to 28V, 36V, and 48V. That enables refills at 45W, 65W, 100W, and up to 140–240W on supporting hardware. Many banks cap input near 18–45W, while premium models reach 60–100W.
Cables And The E-Marker Chip
Many USB-C cables look identical but carry different ratings. A basic cable may top out at 3A. A 5A cable includes an e-marker chip that tells the charger and bank it’s safe to send more current. If your bank and charger support 100W, you still need a 5A-rated cable to see that speed.
Thermal Limits And Taper
Charging follows a constant-current then constant-voltage pattern. The first phase adds most energy fast. Near the top, current tapers to finish safely. That tail adds time you can feel on large packs, which is why a 90% refill can appear much faster than the last few percent.
Estimate With Real Numbers
Grab two details: rated capacity and input rating. Capacity usually prints on the case. Input rating hides near the ports. It may list “USB-C in: 5V3A/9V3A/20V3A (60W).” That’s your ceiling. Match that with a charger and cable that can meet or beat those numbers.
Worked Scenarios
Small commuter pack (10,000mAh): mAh ÷ 1000 × 3.7 → 37Wh. With a 20W charger: 37 ÷ 20 ÷ 0.9 ≈ 2.0–2.2 hours.
Weekend pack (20,000mAh): 74Wh. With a 45W input: 74 ÷ 45 ÷ 0.9 ≈ 1.8–2.0 hours.
Travel-ready near airline limit (≈27,000mAh/99Wh): 99Wh. With a 65W input: 99 ÷ 65 ÷ 0.9 ≈ 1.7 hours; expect ~1.9 hours to finish.
Why Your Result May Differ
- Efficiency: Conversion and heat losses vary by design.
- Taper: The last 10–15% slows.
- Cable swap: A 3A cable caps many setups near 60W.
- Charger sharing: Multi-port bricks divide power.
Charging A Phone, Tablet, Or Laptop From A Bank
“How long will it charge my device?” maps to the same energy math. Compare the bank’s usable Wh to the device battery’s Wh and add a loss budget.
Quick Device Runtime Map
Use these rough totals to plan a day. The table assumes healthy gear, modest screen use, and about 85–90% transfer efficiency.
| Bank Size | Typical Device | What You Get |
|---|---|---|
| 10,000mAh | Modern phone | ~1.8–2.2 full refills |
| 20,000mAh | Phone or small tablet | ~3.5–4.5 phone refills or ~1.2–1.6 small-tablet refills |
| 27,000mAh (99Wh) | Ultrabook at 60W | ~1–1.5 work sessions of light use |
| 30,000mAh | Gaming handheld | ~4–6 hours while playing |
| 50,000mAh+ | High-draw laptop | Partial top-ups unless the bank supports 140W–240W output |
Pick The Right Charger And Cable
Match the bank’s input spec with a charger that meets it on a single port. If the label lists 20V×3A (60W) input, a 65W single-port USB-C PD brick gives headroom. Pair it with a certified 5A cable for anything above 60W.
Standards That Matter
USB Power Delivery set the modern levels for 9V, 15V, and 20V up to 100W. Extended Power Range opened 28V, 36V, and 48V up to 240W. For the spec, see the USB-IF page on USB Power Delivery. For airline watt-hour math used on labels and limits, see the FAA page on lithium-batteries.
Spot And Fix A Slow Setup
- The bank shows “charging” but the time hardly moves. Check the input label; it may be using a low-power path.
- Your charger promises a big number, yet the bank peaks low. Try a different port or a single-port brick.
- Heat near the connector. Swap the cable; weak conductors cause drop and waste.
Worked Table: From Specs To Minutes
This cheat sheet turns common label pairs into time ranges. Numbers assume a healthy cable and about 90% overall efficiency.
| Label On Bank | Use This Charger | Estimated Time |
|---|---|---|
| USB-C in 5V⎓3A (15W) | 18–20W PD | 10,000mAh: ~2.6–3.0h; 20,000mAh: ~5–6h |
| USB-C in 9V⎓3A (27W) | 30W PD | 10,000mAh: ~1.8–2.1h; 20,000mAh: ~3.5–4.0h |
| USB-C in 20V⎓3A (60W) | 65W PD | 20,000mAh: ~1.8–2.0h; 27,000mAh: ~1.7–2.0h |
| USB-C in 20V⎓5A (100W) | 100W PD + 5A cable | 30,000mAh: ~1.2–1.6h; 50,000mAh: ~2.0–2.7h |
| USB-C in 28–48V (EPR) | 140–240W PD + 5A cable | Large laptop banks: often under 90–120 min |
Buyer Notes
Commuters: Pick 10,000–12,000mAh with a 20W input. Small, quick to refill in a car or at a desk.
Travelers: Aim near 27,000mAh/99Wh with a 45–65W input and 65–100W output. That size meets most airline limits and can top a laptop between flights.
Creators And Gamers: Pick banks that advertise 100W–140W output and at least 60W input. Pair with a strong single-port charger and a 5A cable.
Takeaway
Charge time comes down to simple math. Convert to Wh, match the input with a capable charger and cable, then add a small buffer for losses and taper. Do the check once, save it, and plan refills with confidence every trip or long days.