Most portable chargers refill in 2–12 hours, based on capacity (mAh), input watts, and the charger and cable you use.
You came here for charging time you can trust. The short story: the number on the box (mAh) only sets the ceiling. The clock depends on energy in watt-hours, the input wattage your bank accepts, charger speed, cable quality, and the taper phase near full. This guide gives quick ranges first, then shows how to predict your own time with simple math and a few checks.
Typical Charging Time For A Portable Battery Pack
Start with these ballpark ranges. They assume a modern USB-C input and good conditions at room temperature. If your bank takes only 5V/2A over Micro-USB, use the slower column.
| Capacity | 10W Charger | 18W USB-C PD |
|---|---|---|
| 5,000 mAh | 3–5 hrs | 2–3 hrs |
| 10,000 mAh | 6–10 hrs | 3–4 hrs |
| 20,000 mAh | 10–18 hrs | 5–7 hrs |
| 26,800 mAh | 14–22 hrs | 6–9 hrs |
What Actually Sets The Clock
Energy In Watt-Hours, Not Just mAh
The label mAh is only a capacity at the cell’s voltage. Time comes from energy (Wh). Convert with: Wh = (mAh × 3.7) ÷ 1000. A 10,000 mAh pack holds about 37 Wh, and a 20,000 mAh pack about 74 Wh. That’s the energy you need to push back in.
Input Wattage Your Bank Accepts
Many banks accept 10–30 W in. USB Power Delivery (USB-C PD) supports stepped or programmable voltages and much higher ceilings than legacy 5 V charging, so a PD-rated bank paired with a PD charger can refill far faster than a 5V/2A input. Newer EPR tiers even allow higher voltages for laptops and big packs.
The Taper Near Full
Lithium-ion charging runs in two phases: constant current to reach near-full, then constant voltage where current tapers to a small fraction. That last stretch slows the progress bar even with a strong charger. Many specs quote “to 80%” times for this reason.
How To Estimate Your Own Charge Time
You can predict a realistic window with two steps. Use them once and you’ll never guess again.
Step 1: Get The Real Inputs
- Bank capacity in Wh: multiply the mAh rating by 3.7 and divide by 1000.
- Max input power: check the bank’s label near the USB-C port or the spec sheet. Look for “Input: 5V⎓3A, 9V⎓2A, 12V⎓1.5A (18W)” or similar.
- Charger rating: confirm your wall charger can match or exceed that input. A 30 W PD charger can feed an 18 W bank; a 10 W cube cannot saturate a 30 W bank.
- Cable: a C-to-C cable that supports e-marked 5 A isn’t required for 18–30 W, but flimsy or damaged cables can choke current and add hours.
Step 2: Run The Quick Math
Use this handy rule: Time (hours) ≈ Wh ÷ (Charger W × 0.85). The 0.85 factor covers conversion losses and the taper near full. A 37 Wh bank on an 18 W input lands near 37 ÷ (18 × 0.85) ≈ 2.4 hours to fill, with extra time if heat or cables get in the way.
Why Your Result Might Be Slower
Charger Not Negotiating Fast Modes
Fast modes require the right pair. USB-C PD needs a PD-capable charger and cable; Quick Charge has its own handshake. If the link falls back to 5 V only, you’re limited to basic 5–10 W input.
Passive Cables And Port Limits
Ports labeled “USB-A” often cap input to 10 W even if the charger headline says 30 W total. Use the marked USB-C PD port and a C-to-C cable for best results.
Hot Or Cold Conditions
Cells throttle when they’re too warm or too cold. The bank may reduce current to protect itself, stretching the last 20–30% of the refill.
Fast Charging Tech In Plain English
USB-C PD raises voltage in safe steps (5 V, 9 V, 15 V, 20 V, with more under EPR) so the same current moves more power. That’s how you see inputs like 18 W, 30 W, or beyond on modern banks. Quick Charge is a different path that also bumps voltage. Many banks support both so they play nice with a wide range of chargers.
Want the formal spec background? See the USB-IF page on USB Power Delivery. Curious about the slow finish near 100%? Battery University’s primer on charging lithium-ion shows the current taper that adds time at the end.
Specs To Check On The Box
Input Lines
Look for a row that starts with “Input.” Good labels show each voltage and current pair, such as 5V⎓3A, 9V⎓2A, 12V⎓1.5A. Multiply V × A to read watts. If you only see 5V⎓2A, plan for slow refills.
PD, PPS, Or QC Badges
PD covers cross-brand fast modes through USB-C. PPS adds finer voltage steps that keep heat down at higher power. QC is common on older A-port bricks; many banks accept both so you get speed with mixed chargers.
Cell Voltage And Wh Marking
A mAh number alone hides the real energy. Packs that also print watt-hours (Wh) make math and airline checks simple. The label often lists something like “99.9 Wh,” which is under the 100 Wh fly-safe limit for carry-on packs.
Pass-Through And Re-Charge Rate
Some spec sheets list both output watts and input watts. Those are different numbers. You might see “Outputs up to 65 W” and “Input 30 W.” The input figure controls how long your own refill takes.
Charger Wattage Versus Refill Time
Here’s a quick look at how swapping the wall plug changes the wait for two popular sizes. The figures assume capable banks that can accept each listed input, a solid C-to-C cable, and room-temperature charging.
| Charger Rating | 10,000 mAh Bank | 20,000 mAh Bank |
|---|---|---|
| 10 W (5V/2A) | 6–10 hrs | 10–18 hrs |
| 18 W (PD/QC) | 3–4 hrs | 5–7 hrs |
| 30 W (PD PPS) | 2–3 hrs | 3.5–5.5 hrs |
| 45 W (PD) | ~2 hrs* | ~3–4 hrs* |
*Only if the bank’s spec lists a matching 45 W input; many models top out at 18–30 W for charging themselves.
Cable And Port Checklist That Saves Hours
Use USB-C On Both Ends
A direct C-to-C link lets PD engage. A-to-C often locks you to 5 V inputs.
Pick A Wall Plug That Exceeds The Bank’s Input
If the bank says “Input 5–9 V up to 18 W,” any PD brick from 20–30 W is fine. Extra headroom helps when the bank is warm or you’re pass-through charging a phone.
Watch For Total Output Versus Per-Port Output
A 65 W charger with three ports may offer only 20 W on one port when others are in use. If charge time matters, plug the bank into the highest-rated single port.
Real-World Scenarios
Refilling Overnight
Using a 10 W cube, a 10,000 mAh pack typically finishes by morning; a 20,000 mAh pack can run into late morning. Slow, but fine for bedside charging where speed isn’t the goal.
Quick Top-Off Before Leaving
With an 18–30 W PD plug, a 10,000 mAh bank gains a strong chunk in an hour. Larger packs get back into the safe zone fast enough for a day out.
Pass-Through While Powering A Phone
Some banks can charge themselves and a device at the same time. Expect the bank to reserve current for the phone, so the overall refill takes longer than the table values.
Care Habits That Keep Speed Consistent
- Avoid letting the pack bake in a car or on a radiator; heat invites throttling.
- Charge in open air; don’t bury the pack under pillows during a fast refill.
- Partial refills are fine. Li-ion doesn’t need full cycles to stay healthy.
- Replace frayed cables. High resistance steals watts and stretches time.
Troubleshooting Slow Recharges
“My Fast Charger Isn’t Fast”
Match the symbols: PD logo on the charger, USB-C on both ends, and an input spec on the bank that lists 9 V or higher. If any link in the chain is basic 5 V, you’ll see slow times.
“The Last 10% Takes Forever”
That’s the normal taper. Many makers quote an 80% time because the final stretch moves at a crawl to protect the cells.
“It Stops Growing At 99%”
Some banks rest near full and may tick to 100% after a short settle. Unplug and use it; energy is in there.
Quick Calculator You Can Bookmark
Keep this mini recipe handy:
- Convert mAh to Wh (mAh × 3.7 ÷ 1000).
- Find the bank’s max input (W).
- Time ≈ Wh ÷ (Input W × 0.85). Round up a little for warm rooms or flimsy cables.
Upgrade Paths If Time Matters
Pick A Bank With Higher Self-Charge Input
Many mid-range packs cap at 18 W in. Models that accept 30–45 W feed can cut waits by hours, as long as your wall plug and cable match.
Grab A Better Wall Plug
If you own only 5–10 W bricks, a small 30 W PD charger offers a big jump without much cost or size.
Keep One Great Cable In Your Go-Bag
A quality C-to-C cable with e-marker handles high voltage and current and resists wear. It also keeps negotiation stable, which keeps input high.
Takeaway
Charging time isn’t a mystery. Look at energy in watt-hours, match the wall plug to the bank’s input rating, use a solid C-to-C cable, and allow for the gentle finish near full. Do that, and your wait will line up with the tables at the top.