Charging

What is fast charging?

Fast charging is charging with more power than the basic 5 V of USB. The charger, the cable and the device agree on a higher voltage or current, so the battery fills faster, above all in the first part of the charge.

By Cords®Updated 3 November 20263 min read

Cords® Cubical C1 in Electric Orange on a desk against a blue wall

5 Vwhere every USB charge starts

15 Wabove this, EU rules ask for USB Power Delivery

70 %about where charging starts to slow

10 °Cthe most a battery should warm above the room

What counts as fast

There is no single figure. Basic USB power is 5 V. Fast charging raises the voltage, the current or both, so more watts reach the battery.

Volts

How hard the power pushes

Amps

How much of it flows

Watts

Volts times amps: the power

9 V at 3 A is 27 W. 20 V at 5 A is 100 W.

Each device has its own top speed. Apple fast-charges the iPhone Air and iPhone 17e with a 20 W adapter or higher, and the iPhone 17 models with 40 W or higher. So 20 W is fast for one phone and slow for another.

Three things must agree

Charger

Offers the power

Cable

Carries it, up to its rating

Device

Asks for what it can take

The slowest of the three sets the speed. A 100 W charger, a 60 W cable and a phone that takes 27 W charge at 27 W. Swap the phone for a laptop that takes 100 W, and the cable becomes the limit: 60 W.

Why charging slows near full

A lithium-ion charge in two phases: full current until the battery is about 70 % full, then the current eases off and the battery fills more slowly — A charge in two phases. Drawn to show the shape, not measured on a device.

A lithium-ion battery charges in two phases. First it takes full current and fills quickly. From about 70 %, it accepts less, so the current eases off and the last part takes longest.

That is why fast-charging figures are usually given to 50 %.

Power Delivery and Quick Charge

Fast charging needs the charger and the device to speak the same language. Two are common.

	USB Power Delivery	Qualcomm Quick Charge
From	The USB Implementers Forum	Qualcomm
Connector	USB-C	USB-A, then USB-C
Used by	iPhone, Samsung Galaxy, USB-C laptops	Android phones with Snapdragon chips
In the EU	Required above 5 V, 3 A or 15 W	Allowed alongside USB Power Delivery

Quick Charge has moved towards Power Delivery over the years:

2013: Quick Charge 1.0, up to 10 W.
2014: Quick Charge 2.0, at 9 or 12 V, up to 18 W.
2015: Quick Charge 3.0, with voltage in steps of 0.2 V up to 20 V.
2016: Quick Charge 4, which works with USB Power Delivery.
2020: Quick Charge 5, which works with USB Power Delivery PPS.

In the EU, a device covered by the common charger rules that charges by wire above 5 V, 3 A or 15 W must support USB Power Delivery. So a USB Power Delivery charger is the one that works across brands. More in What is USB-C Power Delivery?

Is fast charging bad for the battery?

Heat wears a battery more than speed does. With Power Delivery, the device decides how much power to take, and takes less as it fills.

Battery University advises that a lithium-ion battery should not warm more than 10 °C above the room by the end of a charge, and that it lasts longer when it is not always charged to full.

Charge at room temperature. Lithium-ion should not be charged below freezing.
Use a cable rated for the watts.

Cords® Cubical C1 in Jet Black on a sideboard in a living room — Cubical C1 in Jet Black and in Sand.

Cords® Cubical C1 in Sand on a table beside a lamp — Cubical C1 in Jet Black and in Sand.

Fast charging at the desk

Cylindric UX1 gives up to 100 W from one USB-C port and 165 W across four. Cubical C1 gives up to 65 W from one port. Both use USB Power Delivery 3.1.

Cords® Cylindric UX1 in Jet Black, front, with its four USB-C ports — Cylindric UX1Up to 100 W from one port165 W across fourUSB Power Delivery 3.1See Cylindric UX1

Cords® USB-C Cord A1 in Jet Black: its two USB-C plugs, seen from above — USB-C Cord A1100 W with USB Power DeliveryUSB 2.0 data, 480 MbpsBraided, 1 m or 2 mSee USB-C Cord A1

Questions

Is 20 W fast charging?

For many phones, yes. Apple lists 20 W or higher for fast charging the iPhone Air and iPhone 17e. Larger phones and laptops take more.

Does fast charging damage the battery?

Not in itself. Heat is what wears a battery, and the device controls how much power it takes.

Why is my phone not fast charging?

One of the three is holding it back. Check that the charger supports USB Power Delivery, that the cable is rated for the watts, and that the phone is not hot.