Most power banks refill in 3–12 hours, shaped by capacity, charger wattage, and charging tech.
Planning a trip or a busy day out, and wondering when your portable charger will be ready? The refill time hinges on three things: how much energy the pack can hold, how fast your wall charger can push power, and the charging standard the pack supports. This guide gives you plain-English math, clear tables, and quick wins so you can predict the wait and shave it down without hurting the battery.
Quick Answer And What Changes The Time
Small packs with 5,000–10,000mAh usually top up in 3–6 hours with a 15–20W USB-C charger. Mid-range 20,000mAh models land near 6–10 hours with a 20–30W brick. Jumbo units may need an overnight window unless they accept high-wattage USB-C PD input. The spread comes from capacity, input wattage, cable quality, and heat.
Typical Refill Windows By Capacity And Charger
The table below uses common capacities and realistic PD input levels. Times assume healthy cables and modern cells.
| Bank Size | Charger Input (W) | Expected Refill Time |
|---|---|---|
| 5,000mAh (18.5Wh) | 15–20W | ~2–3 hrs |
| 10,000mAh (37Wh) | 18–20W | ~3–5 hrs |
| 10,000mAh (37Wh) | 30W+ | ~2.5–4 hrs |
| 20,000mAh (74Wh) | 18–20W | ~7–10 hrs |
| 20,000mAh (74Wh) | 30W | ~5–7 hrs |
| 26,800mAh (96Wh) | 30–45W | ~5–8 hrs |
| 26,800mAh (96Wh) | 65–100W (if supported) | ~3–5 hrs |
How Long A Power Bank Takes To Charge: Variables That Matter
Capacity And Wh Matter More Than mAh
Capacity is usually printed in milliamp-hours at 3.7V (the cell’s nominal voltage). For timing, watt-hours (Wh) are clearer. A quick rule: Wh ≈ (mAh × 3.7) ÷ 1000. A 10,000mAh pack holds about 37Wh; a 20,000mAh pack holds about 74Wh. That’s the energy you need to push back in.
Input Wattage Sets The Ceiling
Input power (the number on the bank’s “IN” spec) limits how fast it can refill. If a pack’s USB-C input tops out at 18W, a 65W charger won’t speed it up. Matching the bank’s rated input with a capable wall adapter and quality cable gets you the best case.
The One-Line Math
Use this simple estimate: Time (hours) ≈ Capacity (Wh) ÷ Charger Power (W) × 1.2. The ×1.2 factor covers conversion losses and taper near full charge, which aligns with consumer guidance that adds a small overhead to raw math.
Sample Scenarios You Can Trust
- 10,000mAh bank (≈37Wh) with an 18W USB-C input: 37 ÷ 18 × 1.2 ≈ 2.5 hours. Real-world: 3–4 hours allows for taper and cable losses.
- 20,000mAh bank (≈74Wh) with 20W input: 74 ÷ 20 × 1.2 ≈ 4.4 hours. Real-world: 6–8 hours is common because many units sit closer to 18W and reduce current near 90%.
- 26,000–27,000mAh bank (≈96Wh) with 45W PD input: 96 ÷ 45 × 1.2 ≈ 2.6 hours. Packs that accept higher PD input can reach 80% fast, then slow; brand launches cite rapid top-ups when twin PD bricks are used.
Charging Standard: PD And PPS
USB Power Delivery negotiates voltage and current so the bank can take in more power safely. Modern PD extends up to 240W on the charger side; banks won’t use that entire range, but support for higher PD input levels trims refill time. See the USB-IF’s USB PD overview for the official feature set.
Phones and some banks also speak PPS, which fine-tunes voltage and current during the session for efficiency and heat control. Recent explainers cover how PD and PPS work together to raise safe power transfer.
Cables, Heat, And The Last 10%
A worn cable, a non-e-marked USB-C cable at higher wattage, or a hot room stretches the timeline. Packs also slow near full to protect cells, so the last slice can take longer than the first big chunk.
Turn The Math Into A Plan
Step-By-Step Timing Check
- Read the label: find mAh and the input spec (e.g., “USB-C IN: 5V⎓3A, 9V⎓2A”).
- Convert to Wh: Wh ≈ mAh × 3.7 ÷ 1000.
- Pick your lowest PD input wattage from the label (voltage × amps).
- Run the estimate: Wh ÷ watts × 1.2.
- Add a buffer if charging in a warm space or with a long cable.
When A Bigger Brick Helps
Upgrading the wall charger only helps if the bank’s input spec allows it. A 20W-limited bank won’t take 30W. A bank rated for 45W PD input will reward a 45–65W PD charger with shorter waits. Brand guides and spec sheets point to these ranges and typical 10,000mAh and 20,000mAh times.
Real Charging Outcomes For Phones And Laptops
Refill time for the bank is one side; what you can power on the go is the other. Use these ballpark figures to set expectations. Times assume wired charging and healthy cables.
| Bank Energy (Wh) | Device Type | Typical Results |
|---|---|---|
| 37Wh (10,000mAh) | Smartphone (12–15Wh battery) | ~1.5–2 full charges; 0–50% in ~30–45 min with 18–20W PD |
| 74Wh (20,000mAh) | Tablet (25–30Wh battery) | ~2 charges; top-ups are faster with PD or PPS |
| 96Wh (26,800mAh) | Ultrabook (50–60Wh battery) | ~1–1.5 charges; best with 45–65W PD output support |
Fast Standards In Plain Terms
USB PD Levels
PD defines set voltage steps and a power envelope that devices negotiate in real time. That clarity makes timing predictable: a pack that accepts 30W PD input can cut hours versus a 15–18W limit, while newer PD profiles expand the ceiling for devices that need it.
Why PPS Can Trim Heat
PPS adjusts voltage in small steps so the charger tracks what the cells want. Less wasted heat means steadier current before taper. That steadiness can trim minutes in the mid-charge band.
Tips To Speed Up A Refill Safely
- Use a PD wall charger that matches the bank’s rated input. Going far above the rating won’t add speed unless the bank accepts it.
- Pick the right cable. For 60W and up, use an e-marked USB-C cable. Shorter runs waste less power as heat.
- Keep it cool. Charge on a hard surface out of direct sun. Warm packs slow near the top.
- Skip pass-through when you’re in a hurry. Most banks throttle when charging themselves and another device at once.
- Know air-travel limits. Lithium packs up to 100Wh fly in carry-on; 101–160Wh may need airline approval; no packs in checked bags. See the FAA’s PackSafe lithium battery rules.
Why The Last Bit Takes Longer
Most banks follow a constant-current, then constant-voltage pattern. You’ll see fast progress to roughly 70–80%, then a slower crawl. That’s normal cell protection behavior with lithium-ion packs and part of the overhead reflected in the timing math.
Small Magnetic And Wireless Packs
Magnetic puck-style units trade speed for convenience. Wireless output around 7.5–15W means device top-ups take longer, and those same units often accept modest input when you refill them. Newer Qi2-ready models improve speeds and add a USB-C port for faster wired sessions. Recent product briefs cite 15W wireless and 20W wired as a common split.
When Big Numbers Don’t Add Up
mAh vs. Wh And Conversion Losses
The pack stores energy at ~3.7V, but output steps up to 5–20V for your gadgets, and input steps up from your wall brick. Each conversion wastes a slice, so the energy you put in and the energy you get out don’t match one-to-one. That’s why estimates include a loss factor and why brand guides anchor 10,000mAh near 3–6 hours depending on the charger.
Spec Sheet Red Flags
- “100W output” with tiny input. If input tops out at 18W, refills still take time even if output can burst higher to charge a laptop.
- Old micro-USB charge port. These ports usually cap at 10W or less. USB-C PD intake is the better bet.
- No PPS mention on packs aimed at Android fast charge. You’ll still refill, but heat and throttling may show up sooner.
Troubleshooting Slow Recharges
- Cable swap. Try a short, known-good USB-C cable rated for your wattage.
- Port choice. Some banks have a single high-input USB-C and slower legacy ports. Use the one labeled for PD IN.
- Wall adapter check. Confirm its wattage and that PD is present; generic 5V/2A bricks stall at 10W.
- Room temp. Cool the area and let the bank rest before charging if it feels warm.
Cheat Sheet: Match Bank And Charger
Pair your bank’s rated input with a charger that can deliver that wattage under PD. This quick list maps common inputs to simple picks.
| Bank Input Rating | Use This Charger | What To Expect |
|---|---|---|
| 18–20W PD IN | 20W PD USB-C | Best speed for 5k–10k banks; mid-range still fine |
| 30W PD IN | 30–45W PD USB-C | Good pick for 10k–20k; trims hours on larger packs |
| 45–60W PD IN | 65W PD USB-C | Fast refills on 20k–27k banks; watch cable rating |
Where The “Fast” In Fast Charging Comes From
PD raises the voltage and current in agreed steps so both sides stay inside safe limits while moving energy quicker. The latest PD profiles extend the ceiling for laptops and docks, and banks that accept higher PD input can refill a big pack before lunch rather than overnight. Official materials spell out the step-up in power levels and the adjustable-voltage mode used by PPS phones.
Make Your Pack Last While Keeping Speed
- Charge with PD and a capable cable to reach the rated intake without stress.
- Avoid stacking heavy loads during refill; pass-through lowers intake speed.
- Store around half-full if you won’t use it for weeks.
- Travel tip: check airline watt-hour limits before you pack; the FAA page linked above reflects current rules.
Bottom Line For Timing Your Refill
Find the input wattage on the label, convert mAh to Wh, and run Wh ÷ W × 1.2. That single step predicts the window far better than guesswork. Match the bank with a PD charger and solid cable, keep it cool, and you’ll stay in the faster half of the ranges shown here. Brand guides and current PD explainers back the 3–12 hour spread across common sizes, and high-input models can drop well below that with the right brick.