Power bank charging time ranges from 1–8 hours, set by capacity (Wh), input wattage, and a 10–20% energy loss in the charge path.
Here’s the plain math and the smart tweaks that trim hours off a recharge. You’ll see how battery size, the charger’s wattage, the bank’s input rating, and the cable all set the pace. Then you’ll get clear tables with real-world times, plus quick fixes when charging feels slow.
Quick Formula For Power Bank Recharge Time
Use this two-step method:
- Convert capacity to watt-hours (Wh):
Wh = (mAh × 3.7) ÷ 1000. Most lithium packs inside banks sit near 3.7V. - Estimate time:
Time (hrs) = Wh ÷ Charger_Watts × 1.15. The 1.15 factor covers typical heat and conversion loss.
That 1.15 factor is a middle-ground estimate for everyday gear. Some stacks sit near 1.10 with efficient silicon and short cables; others lean closer to 1.20.
Broad Time Estimates By Size And Input Power
This table gives ballpark wall-to-full times. It assumes the bank’s USB-C input allows the listed wattage and you’re using a matching cable and charger. If your bank caps input below your charger’s rating, use the lower number.
| Capacity (mAh @3.7V ≈ Wh) | Input Power (W) | Est. Full Charge Time |
|---|---|---|
| 5,000 ≈ 18.5 Wh | 10 W | ~2.1 hours |
| 5,000 ≈ 18.5 Wh | 20 W | ~1.0 hour |
| 10,000 ≈ 37 Wh | 10 W | ~4.3 hours |
| 10,000 ≈ 37 Wh | 18–20 W | ~2.1 hours |
| 10,000 ≈ 37 Wh | 30 W | ~1.4 hours |
| 20,000 ≈ 74 Wh | 18–20 W | ~4.3 hours |
| 20,000 ≈ 74 Wh | 30 W | ~2.8 hours |
| 20,000 ≈ 74 Wh | 45–60 W | ~1.5–1.9 hours |
| 24,000 ≈ 88.8 Wh | 30 W | ~3.4 hours |
| 24,000 ≈ 88.8 Wh | 45–60 W | ~1.9–2.3 hours |
| 26,800 ≈ 99 Wh | 30 W | ~3.8 hours |
| 26,800 ≈ 99 Wh | 60–100 W | ~1.1–1.9 hours |
How Long Does A Power Bank Take To Recharge? Practical Math
Let’s walk through one set. A 20,000 mAh pack holds about 74 Wh. With a 20 W wall charger, time is 74 ÷ 20 × 1.15 ≈ 4.3 hours. Swap to a 45 W charger and a bank that accepts it, and you’re near 74 ÷ 45 × 1.15 ≈ 1.9 hours. Same battery, different input, big swing.
Two parts gate your speed: the charger’s wattage and the bank’s input spec. The slower piece wins. If your bank lists “Input: 5V=3A, 9V=2A, 20V=3A,” it can drink up to 60 W with the right protocol and cable. If it says only “5V=2A,” you’re stuck near 10 W.
Why The Last 10–15% Feels Slow
Most banks use a constant-current phase, then a constant-voltage taper near the top. That taper cuts current to protect the cells, so the charge meter creeps. Hitting 80% is quick; the final stretch takes more minutes per percent. This is normal lithium behavior.
Match The Charger, Port, And Cable
The fastest path pairs a PD-capable USB-C charger, a full-rated USB-C cable, and a bank that advertises a matching input wattage. USB Power Delivery now spans high power ranges over the Type-C connector, and many modern banks accept those higher steps. Link the trio and the numbers in the table turn real.
Port Labels You’ll See
- USB-C PD (including PPS): common on new banks and chargers. Look for 20 W, 30 W, 45 W, 60 W, 100 W, or more on the input spec.
- Old micro-USB: usually limited to 10 W or less. Good for overnight, not for quick turnarounds.
- Dual-port banks: some models let you charge the bank from USB-C while it powers a device on USB-A; speed can dip when doing both.
Choosing The Right Wall Charger
Pick a wattage that clears your bank’s max input. If the bank tops out at 30 W, a 65 W brick won’t fill it faster than 30 W; it just has headroom when you charge other gear. If the bank supports 45–60 W input, stepping up from a 20 W cube cuts hours.
| Charger Wattage | Port Standard | Best Use |
|---|---|---|
| 18–20 W | USB-C PD | Small and mid banks; travel light; okay overnight for larger packs. |
| 30 W | USB-C PD | Faster refills for 10–20k mAh; good single-port pace. |
| 45 W | USB-C PD / PPS | Great match for 20–26.8k mAh banks that advertise 45 W input. |
| 60–100 W | USB-C PD / PPS | High-end banks with big input caps; trims time on 24–26.8k mAh. |
| 140–240 W | USB-C PD (newer PD steps) | Only helps if the bank lists a matching high input; otherwise no gain. |
Real-World Variables That Add Or Cut Time
Cable Limits
Not all USB-C cables pass high current. A cable rated for 3A at 20V supports up to 60 W; 5A e-marked cables support up to 100 W and beyond. A weak cable forces the stack to step down, which slows the refill.
Heat And Venting
Charging produces heat. A bank stuffed under pillows or in a hot car may throttle. Give it airflow and a flat surface. A cooler pack charges closer to its rated pace.
Charging While Using The Bank
Pass-through looks handy, but the input power now splits between the cells and your device. If you want speed, let the pack charge alone.
State Of Charge At Plug-In
From 10% to 80% flies compared with 80% to full. If you don’t need 100%, a 30–60 minute top-up can be enough for a flight or commute.
Fast Protocols And Where They Help
USB-C PD is the common fast path for banks. Many chargers add PPS, which fine-tunes voltage and current. When both sides speak the same profile, the bank can draw closer to its max input rating. Brands also advertise vendor terms, but the label isn’t the goal; the input watts are.
Want extra reading on the standard itself? See the USB Power Delivery page for the current power ranges and connector details.
Safe Limits And Ratings You’ll See On The Label
Most travel-size banks list their energy in Wh along with charge and output specs. You might see “99 Wh” on a 26,800 mAh model because the Wh value uses the internal pack voltage, not 5V USB output. That’s normal. The Wh figure also appears in airline guidance since it’s the standard measure for lithium packs. If you’re curious about the definition, check the IATA explanation of the Watt-hour rating.
Sizing Your Setup For A Specific Time Goal
Pick your target window, then back-solve:
- List the bank’s Wh. A common 20,000 mAh pack is ~74 Wh.
- Pick a charger that meets or beats the bank’s input cap. If the bank takes 45 W input, use a 45–65 W PD charger.
- Use a rated cable. For ≥60 W, choose a 5A e-marked USB-C cable.
- Plug directly into the wall. Avoid old hubs and USB-A sockets.
Example targets:
- About 2 hours with a 20,000 mAh pack: You’ll want ~45 W input on the bank and a 45–65 W PD wall charger.
- About 1 hour with a 10,000 mAh pack: A bank that accepts ~30 W input and a 30 W PD charger gets you there.
Troubleshooting Slow Recharges
The Bank Never Passes 10–12 W
Check the fine print. If the input spec lists only 5V numbers, the bank isn’t set up for higher PD steps. You’ll need a model with a higher input rating to speed things up.
The Charger Is Strong, But Time Hasn’t Improved
Swap the cable. Then try a different wall outlet. Confirm the USB-C port you used is labeled with the higher PD step. Some multi-port chargers split power across ports.
The Display Shows Fast Watts, Yet The Clock Says Otherwise
Displays often show instant power, not the average over a session. During the voltage-hold phase near full, the amps taper, so the average rate falls. Short runs to 70–80% keep you inside the faster slice.
When Bigger Chargers Don’t Help
A 100 W brick can’t speed a bank that caps input at 18–20 W. The bank sets the ceiling. A higher-rated brick still makes sense if you also charge laptops, but it won’t shrink this bank’s refill below its listed input.
Tips To Hit Your Time Targets
- Buy on input watts, not just output watts. Many listings shout about 140 W output. Scan the input line; that’s your refill speed.
- Pack one quality cable. A single 5A e-marked USB-C cable covers nearly every fast-charge case.
- Keep the bank cool during the session. A room-temp surface helps the controller stay at higher current.
- Skip pass-through during refills. Let the pack drink first; then charge your phone.
Capacity, Travel, And Labels
Many travel-size models stay under ~100 Wh, which aligns with common airline rules for carry-on packs. The label may show both mAh and Wh, and the Wh uses the internal cell voltage. That’s why a 26,800 mAh bank often reads near 99 Wh on the back.
FAQ-Free Wrap-Up: Make Your Plan
Match the bank’s input spec with a PD wall charger and a rated cable. Convert mAh to Wh, divide by watts, and add a small loss factor. That gives you a trustworthy window. If the number feels long, the upgrade lever is simple: choose a bank with a higher input rating, then feed it with a charger and cable that can deliver.