What Real‑World Capacity Remains After 22.5W PD Use?
Updated 2026-09-29 · Power Bank Guide
When you see a power bank advertised as "22.5W PD" you might wonder how much of that advertised capacity actually ends up in your phone. In this guide we break down the math behind a 20,000 mAh (≈74 Wh) bank, explain the difference between mAh and watt‑hours, and show you the real‑world capacity you can count on after 22.5W PD use.
Understanding Capacity: mAh vs. Watt‑Hours
Manufacturers usually quote capacity in milliamp‑hours (mAh) because it’s a familiar number for phone batteries. However, mAh alone doesn’t tell you the energy stored; you need the cell voltage. Most lithium‑ion cells inside power banks run at a nominal 3.7 V. The conversion is simple:
- Watt‑hours (Wh) = (mAh ÷ 1,000) × voltage
- For a 20,000 mAh bank: (20,000 ÷ 1,000) × 3.7 V ≈ 74 Wh
This 74 Wh figure is what airlines use to enforce the 100 Wh carry‑on limit, so a 20,000 mAh bank is comfortably flight‑safe.
Real‑World Efficiency: What Capacity Remains After 22.5W PD Use?
Power conversion isn’t 100 % efficient. Typical boost‑converter circuits lose 30‑40 % of the stored energy, especially when delivering higher wattage like 22.5 W Power Delivery (PD). A realistic efficiency range is 60‑70 %.
Applying a 65 % average efficiency to our 74 Wh bank gives:
Usable energy ≈ 74 Wh × 0.65 ≈ 48 Wh
That’s the amount of energy that will actually reach your device after the 22.5W PD conversion.
How Fast Is 22.5W PD in Practice?
USB‑C Power Delivery negotiates voltage and current to reach the requested wattage. A 22.5W PD charger typically operates at 5 V × 4.5 A, 9 V × 2.5 A, or 15 V × 1.5 A. The exact speed depends on the phone’s PD profile:
- iPhone 17 Pro Max: Supports up to 20 W, so 22.5W PD will charge at the phone’s max 20 W – roughly 50 % charge in 30 minutes.
- Samsung Galaxy S24 Ultra: Accepts up to 25 W, so it will draw the full 22.5 W, reaching 0‑80 % in about 35 minutes.
- Google Pixel 8 Pro: Limited to 18 W, so it will charge slightly slower than the bank’s maximum.
In short, 22.5W PD is fast enough to give most flagship phones a usable charge in under an hour, but it won’t magically double the speed of a 15 W charger.
How Many Full Charges Can You Expect?
Take a typical phone battery as an example:
- iPhone 17: 3,300 mAh ≈ 12 Wh
- Samsung Galaxy S24: 5,000 mAh ≈ 18 Wh
- Google Pixel 8: 4,800 mAh ≈ 17 Wh
Divide the usable 48 Wh by the phone’s battery Wh and you get a realistic charge count:
- iPhone 17 – 48 Wh ÷ 12 Wh ≈ 4 full charges
- Galaxy S24 – 48 Wh ÷ 18 Wh ≈ 2.5 full charges
- Pixel 8 – 48 Wh ÷ 17 Wh ≈ 2.8 full charges
These numbers assume a single‑device charge cycle and a 65 % efficiency. Mixing devices or using the power bank for other accessories (headphones, flashlights) will reduce the count.
Why the INIU 20000 mAh Portable Charger Is a Good Pick
The INIU 20000 mAh Portable Charger (Flight‑Safe) checks all the boxes we’ve discussed. Its 74 Wh rating stays well under the 100 Wh airline limit, and the built‑in 22.5W PD port delivers the fast‑charging speeds we outlined. The package includes a USB‑C cable and a handy flashlight, making it a compact, all‑in‑one solution for travelers who need reliable, real‑world capacity on the go.
Tips for Getting the Most Out of a 22.5W PD Power Bank
- Charge the bank itself with a wall charger that matches its input rating. Using a 5 V/2 A charger will fill the bank slower and waste less of its internal capacity.
- Avoid deep discharge. Stopping use at around 20 % battery prolongs lifespan and keeps the usable Wh closer to the spec.
- Match voltage. If your phone can accept 9 V PD, use that setting; it reduces current loss and improves overall efficiency.
- Keep cables short and high‑quality. Poor cables add resistance, lowering the effective wattage delivered.
FAQ
Is a 20,000 mAh power bank really 74 Wh?
Yes. The conversion uses the internal cell voltage (3.7 V): 20,000 mAh ÷ 1,000 × 3.7 V ≈ 74 Wh. This is the figure airlines reference for carry‑on limits.
Will 22.5W PD charge my phone faster than a 15W charger?
Generally yes, if your phone supports the higher wattage. A 22.5W PD charger can deliver up to 22.5 W, but the phone will only draw what its PD profile allows. Most modern flagships will see a noticeable speed bump.
How many times can I charge a tablet with a 20,000 mAh bank?
Tablet batteries range from 30‑40 Wh. Using the same 65 % efficiency, a 48 Wh usable pool will give roughly 1‑1.5 full charges for a 30 Wh tablet, or about one full charge for a larger 40 Wh model.