How Does Fast Charging Work? Here’s Every Single Standard Compared

How Does Fast Charging Work?

Processors. RAM. Screens. They’re the way millions of people choose a smartphone to buy. But in recent years, another factor — fast charging — has slowly made its way to the fore. Who doesn’t want a smartphone that can charge in minutes instead of hours?

If only it were that simple. Charging standards are a complicated mix of chemistry and physics, and each have their own sets of limitations and poorly publicized incompatibilities. To make matters worse, phone-makers tend to slap confusing labels on otherwise straightforward components.

So how does fast charging work? Take a deep breath. Our guide to the most popular wireless charging standards on the market breaks them down to their most basic level. Here’s everything you need to know about Samsung Adaptive Fast Charging, Qualcomm Quick Charge, OnePlus Dash Charge, and more.

The basics

How fast charging works

Before we dive into the weeds, let’s start with the fundamentals.

Every smartphone has a battery, and every battery delivers power in more or less the same way.

How Does Fast Charging Work?

Cells consisting of two electrodes (one positive and one negative) and an electrolyte, catalyze reactions that convert compounds into new substances. Over time, ions — atoms with too few or too many electrons — form in the electrodes, driving a flow of electrons to the battery’s negative outer terminal and supplying your phone with an electric charge.

In nonrechargable batteries, those chemical reactions occur only once. But in the rechargeable lithium-ion batteries that power smartphones, the reactions are “reversible.” When the battery discharges, the chemical reaction produces electricity, and when the battery recharges, the chemical reactions absorb power.

Fast charging

So we’ve established how batteries charge and discharge. But to understand how fast charging works, you have to know a bit about something called a charge controller.

A quick side note:

Since we’ll be referring to volts, amps, and watts in the course of our discussion, here’s a refresher. Volts are a measure of voltage, amps are a measure of current, and watts are a measure of electrical power. A common analogy is a garden hose: Volts are equivalent to the water pressure in the hose; the current is equivalent to the flow rate; and wattage is equivalent to the volume of the spout’s spray. Watts, then, are the product of volts and amps — volts (V) times amps (A) equals watts (W).

Greater current and higher voltages charge batteries faster, but there’s a limit to what they can take.

Smartphone batteries charge when a current passes through them. Greater current and higher voltages charge batteries faster, but there’s a limit to what they can take. The charge controller (IC) protects against dangerous spikes in current.

The controller chip regulates the overall flow of electricity into and out of the battery. Generally speaking, lithium-ion controllers define the current (in amps) at which the battery charges by measuring the battery’s cell current and voltage, and then adjusting the current flowing in. Some use a DC to DC converter to change the input voltage, and fancier integrated circuits adjust the resistance between the charger input and the battery terminal to ramp the current flow up or down.

The amount of current the charge controller draws is generally dictated by the phone’s software.

USB charging standards


Voltage Current Max Power
USB 1.0 5V 0.5A 2.5W
USB 2.0 5V 0.5A 2.5W
USB 3.0 5V 0.5A/0.9A 4.5W
USB 3.1 (USB-C + USB-PD) 5-20V 0.5A/0.9A/1.5A/3A/5A 100W

Unless you’re still rocking a Palm Pilot from the early ’90s, chances are your smartphone recharges via USB cable. There’s a really good reason: Besides the fact that USB cables are relatively easy to find these days, USB has a really robust, well-defined charging standard called the USB Power Delivery Specification.

The USB Implementers Forum specifies four flavors in total, one for each corresponding USB specification: USB 1.0, 2.0, 3.0, and 3.1.

A typical USB 1.0 and 2.0 plug can deliver up to 5V/0.5A (2.5W).

USB types

That’s the charging rate of a typical phone, and it doesn’t amount to a lot of power. An iPhone charging at 2A over USB uses 5V x 2A = 10W. The average incandescent lightbulb, by comparison, draws about 40W of power.

By default, USB 3.0 ports push 5V/0.9A (4.5W).

USB-C, the oval-shaped reversible plug on newer smartphones, is a different animal altogether. It’s technically capable of carrying the USB 2.0 spec, but most manufacturers opt for USB 3.1, which can potentially deliver a much higher voltage.

Many USB 3.1 devices take advantage of the USB Power Delivery (USB-PD) spec, which has a maximum power output of 20V/5A (100W). Smartphones don’t typically draw that much power — manufacturers commonly stick with a lower amperage (like 3A), but it’s a boon for USB-C laptops like the MacBook Pro and Google Chromebook Pixel.

Slightly complicating things is the Battery Charging Specification, which deals specifically with power drawn from a USB port for charging. The most recent spec, Rev 1.2, defines three different sources of power: Standard downstream port (SDP), charging downstream port (CDP), and dedicated charging port (DCP). CDP, the spec in modern smartphones, laptops, and other hardware, can supply up to 1.5A.

Fully compliant smartphones and chargers respect the limits of USB 2.0 and BC1.2, but not all phones and chargers are compliant. That’s why, generally speaking, smartphones always default to the lowest charging speed.

The USB specs are more like guidelines than dictum, though. Fast charging standards like Qualcomm’s Quick Charge and Samsung’s Adaptive Fast Charging exceed the USB spec’s voltage parameters, but on purpose — that’s why your phone is able to recharge in minutes, rather than hours.

Fast charging standards: What’s the difference?

Apple fast charging

Julian Chokkattu/Digital Trends


Voltage Current Max Power
USB-PD 14.5V 2A 29W


  • USB-PD, an industry standard, works with a growing number of devices.


  • You’ll have to shell out a few bucks to take advantage — Apple doesn’t include USB-PD-compatible chargers in the box.

The Apple iPhone XS, iPhone XS Max, iPhone XR, iPhone X, iPhone 8, and iPhone 8 Plus implement USB-PD, the same industry standard used by the iPad Pro, the 12-inch MacBook, Google’s Chromebook Pixel, and Lenovo’s X1 Carbon. Inter-compatibility is its biggest advantage — USB-PD doesn’t require any special cables or wall adapters.

Supported outputs, cables, and adapters

You’ll have to shell out for accessories if you want to take advantage of the iPhone’s USB-PD compatibility, because Apple doesn’t pack USB-C cables or adapters in the box. And you’ll need to buy a Lightning to USB-C cable that supports USB-PD — if you use a standard Lightning cable with a USB-C to USB-A adapter, the charger will default to the lowest wattage.

Here’s what Apple recommends:

  • Apple 29W, 61W, or 87W USB-C Power Adapter.
  • A comparable third-party USB-C power adapter that supports USB Power Delivery (USB-PD).

Charging speed

No matter which USB-C charger you buy, you’ll have to put up with hard-coded safety limits in your iPhone. Fast charge kicks in when the capacity is between 0 and 79 percent, but stops when it reaches 80 percent.

If you don’t mind forking over a few extra dollars for charging accessories, you get much faster charging than you would otherwise. The fast charging iPhones can charge from 0 to 50 percent in 30 minutes using USB-PD.

Qualcomm Quick Charge

Julian Chokkattu/Digital Trends


Voltage Current Max Power
Quick Charge 1.0 5V 2A 10W
Quick Charge 2.0 5V/9V/12V 1.67A/2A 18W
Quick Charge 3.0 3.6V – 20V (200mV increments) 2.5A/4.6A 18W
Quick Charge 4.0 N/A N/A N/A
Quick Charge 4.0+ 5V/9V (USB-PD), 3.6V – 20V (200mV increments) 3A (USB-PD), 2.5A/4.6A 27W (USB-PD)


  • One of the most widely implemented charging standards.
  • Backwards compatible with older versions of Quick Charge.
  • Built-in safety features prevent overheating and short circuiting.


  • Quick Charge 3.0 isn’t USB-PD compliant.

Chipmaker Qualcomm’s Quick Charge is one of the most widely implemented charging standards on the market. That’s no mistake — it’s an optional feature of Qualcomm system-on-chips like the Snapdragon 845, 835, 820, 620, 618, 617, and 430, which power phones like the Samsung Galaxy Note 9, Google Pixel 3, and LG V40 ThinQ. But the technology isn’t tied to Qualcomm’s Snapdragon processors — any smartphone manufacturer is free to license Quick Charge’s power controller technology.

Tech specs and compatible adapters

Quick Charge achieves fast charging by upping the charging voltage, which in turn boosts the wattage. Quick Charge 4.0 support is still very rare right now. Quick Charge 3.0’s voltage range is 3.6V minimum and 20V maximum, which Quick Charge 3.0 increments or decrements using Intelligent Negotiation for Optimum Voltage (INOV) to identify the most efficient voltage at any giving point during charging. At its peak voltage, Quick Charge 3.0 can deliver 18W of power.

Quick Charge 4 and newer have the added bonus of compatibility with USB-PD chargers, but Quick Charge 3.0 and older only work with Quick Charge-certified accessories. Still, Quick Charge’s ubiquity means there are plenty to choose from. Qualcomm’s website has a partial list of the most popular options.

Charging speed

Qualcomm claims the latest version of Quick Charge 4+ can recharge smartphones to 50 percent in just 15 minutes. The more ubiquitous Quick Charge 3.0 delivers about 50 percent capacity in half an hour.

In our testing, Quick Charge 3.0-compatible phones like the LG G5 took about 1 hour and 18 minutes to reach 100 percent.

Safety measures

Quick Charge’s intelligent thermal balancing moves current via the coolest path, and device sensors monitor the case and connector temperatures to prevent overheating and short-circuiting.

Samsung Adaptive Fast Charging

Julian Chokkattu/Digital Trends


Voltage Current Max Power
Samsung Adaptive Fast Charging 5V/9V 2A 18W


  • Built into all Samsung devices.
  • Compatible with Quick Charge 2.0.


  • Tends to be conservative.

Samsung’s Adaptive Fast Charging is exclusive to Galaxy devices like the Galaxy S9 and Note 8. Unlike Quick Charge and other competing fast standards, it’s fully compatible with Exynos, the system-on-chip commonly found in international variants of Samsung’s devices.

Tech specs and compatible adapters

Samsung’s Adaptive Fast Charging has a theoretical peak of 9V/2A (18W), but tends to be a bit more conservative in practice. Tapping into Adaptive Fast Charging’s speeds requires buying a certified charger, but most Samsung devices support Quick Charge-compatible accessories.

Charging speed

Samsung doesn’t publish charging times for Adaptive Fast Charging. But in our testing, the Galaxy S8, which has a 3,000mAh battery, took about two hours to fully recharge. Barring a revision to the Adaptive Fast Charging standard, that’s about the charging time you can expect for comparable devices.

Safety measures

Adaptive Fast Charging technical stats are hard to come by, but anecdotally speaking, it’s on the conservative side. According to XDA’s detailed analysis of fast charging standards, the Galaxy S8 Plus maintains the coolest temperature of any fast-charging flagship on the market.

Motorola TurboPower

Julian Chokkattu/Digital Trends


Voltage Current Max Power
TurboPower 15 9V/12V 1.2A/1.67A 15W
TurboPower 25 5V/9V/12V 2.15A/2.85A 25W
TurboPower 30 5V 5.7A 28.5W


  • Built into all Motorola devices.
  • Compatible with Quick Charge 2.0.


  • Not as fast as some charging standards.

Motorola’s TurboPower standard, a tweaked version of Quick Charge 2.0, ships on Motorola devices like the Moto Z2 Force and Moto G6 Plus.

Tech specs and compatible adapters

TurboPower adapters come in three flavors: TurboPower 15, TurboPower 25, and TurboPower 30. The fastest, TurboPower 30, delivers 5V and up to 5.7A for roughly 28.5W of power.

There’s more to TurboPower than the charger. Motorola says it works with manufacturers to design custom batteries, and that its power management software monitors battery state and health, then adjusts the incoming charge accordingly.

Much like Samsung Adapative Fast Charge, you don’t need a TurboPower adapter in order to fast charge a TurboPower-equipped smartphone. Motorola’s charging standard is compatible with any Quick Charge 2.0 (or newer) adapter.

Charging speed

Motorola claims TurboPower 30 can deliver up to 15 hours of battery life in 15 minutes.

Safety measures

TurboPower’s thermal management hardware is designed to avoid charging slowdowns due to heat, Motorola says, and to maintain a steady and fast charging rate.

MediaTek Pump Express


Voltage Current Max Power
MediaTek Pump Express 2.0+ 5V – 20V (0.5V increments) 3A/4.5A+ 15W
MediaTek Pump Express 3.0 3V – 6V (10-20mV increments) 5A+ 25W/30W


  • Built-in safety measures prevent overheating, short circuiting.
  • Compatible with Quick Charge 2.0.


  • Potentially slower than some standards.

MediaTek, a Taiwan-based chip manufacturer primarily focusing on budget and midrange devices, has its own charging standard: Pump Express. Pump Express 2.0+ and Pump Express 3.0, the two newest revisions, coexist — Pump Express 2.0 targets lower-cost MicroUSB and USB-C devices, and Pump Express 3.0 targets high-end USB-C phones.

Tech specs and compatible adapters

Pump Express + 2.0 charges between 5V and 20V versus Pump Express 3.0’s 3V – 6V, which might sound like an advantage. But Pump Express 2.0+ maxes out at 4.5A compared to Pump Express 3.0’s 5A+, and charges in three stages — Regular, Turbo 1, and Turbo 2 — the fastest of which only supports 15W (1.67A).

Pump Express 3.0 has other advantages over Power Express 2.0. It’s compatible with any USB-PD adapter that supports 3V to 6V at 5A+, and any cable that supports 5A.

Charging speed

Pump Express 3.0 devices can charge up to 75 percent in 20 minutes, according to MediaTek. Pump Express 2.0+ devices take about 30 minutes to reach the same capacity.

Safety measures

Pump Express implements more than 20 safety mechanisms to prevent short-circuiting, MediaTek says. System-on-chip technology from Richtek, a company it recently acquired, protects against fluctuating battery and device temperature.

OnePlus Dash Charge and Oppo Vooc

Andy Boxall/Digital Trends


Voltage Current Max Power
Dash Charge 5V 4A 20W
Oppo Vooc 5V 5A 25W


  • Keeps phones cooler.
  • One of the fastest charging standards.
  • Adapters included with compatible smartphones.


  • Highly proprietary.

Shenzhen, China-based OnePlus licenses Dash Charge from Oppo. It’s based on Oppo’s VOOC (Voltage Open Multi-Step Constant-Current Charging) system, and is a headline feature in the OnePlus 6T and every other OnePlus phone back to the OnePlus 3.

Tech specs and compatible adapters

Dash Charge operates at a peak of 5V/4A (20W), slightly lower than Vooc’s 5V/5A (25W). By bumping the charger’s amperage instead of the voltage, it’s able to achieve a more even distribution of electrical current at higher levels. That’s thanks to a special wall adapter that modulates the amperage in real time. A microcontroller monitors charge level and syncs with the phone’s circuitry to regulate voltage and current, and a custom-designed cable delivers greater current while minimizing power fluctuations.

It’s all proprietary. Dash Charge works only with OnePlus phones and compatible wall adapters and car chargers. Dash Charge-certified external batteries are hard to come by, and OnePlus’ fast charging standard doesn’t work with off-the-shelf USB cables — Dash Charge cables are slightly thicker to accommodate the extra voltage.

You won’t have to shell out extra if you buy a OnePlus phone, though. Every OnePlus smartphone comes with a Dash Charge-compatible wall adapter and charging cord.

Charging speed

OnePlus rates Dash Charge at 60 percent capacity in 30 minutes, a stat that a number of publications have corroborated. In our testing, the OnePlus 3 charged from 2 percent to 100 percent in 1 hour and 14 minutes. And XDA found that Dash Charge was 10 minutes quicker than every fast charging standard it tested, including Quick Charge and Adaptive Fast Charging.

Oppo claims Vooc-enabled phones can charge to 75 percent in 30 minutes.

Safety measures

Dash Charge is designed to dissipate heat quickly. Because the charger transforms the high voltage from the adapter’s power source into a lower voltage, most of the heat from the conversion never reaches the phone, and the consistent current reduces the potential for thermal throttling.

Dash Charge-compatible devices also have heat management and dissipation hardware that undergo a thorough five-point safety check.

Huawei SuperCharge


Voltage Current Max Power
Huawei SuperCharge 4.5V/5V 4.5A/5A 25W


  • Compatibility with USB-PD.
  • Thorough safety measures.
  • Adapters included with compatible smartphones.


  • Potentially slower than some standards.

SuperCharge, Chinese smartphone maker Huawei’s proprietary charging standard, is built into phones like the Huawei Mate 20 Pro, Mate 9 and the Huawei P10. It’s is somewhat akin to Quick Charge in that it uses higher-than-average voltages to achieve faster charging, but there’s slightly more to it than meets the eye.

Tech specs and compatible adapters

SuperCharge automatically adapts the incoming wall voltage and current based on the condition of the phone’s battery and the phone’s internal temperature. SuperCharge-compatible wall adapters and car chargers support three charging modes — 5V/2A, 4.5V/5A, and 5V/4.5A (up to 22.5W) — and use an in-charger chipset to regulate voltage, eliminating the need for heat-producing in-phone voltage transformation.

Unlike proprietary charging standards like Pump Express and Dash Charge, Supercharge is compatible with USB-PD. That’s thanks to Huawei’s Smart Charge protocol, which intelligently switches between charging modes depending on which charging adapter is plugged in.

Tapping into Huawei’s SuperCharge technology requires buying a compatible wall adapter, but native compatibility with Qualcomm’s Quick Charge standard means any SuperCharge-compatible devices can take advantage of Quick Charge. Every SuperCharge-compatible smartphone comes with a compatible wall adapter.

Charging speed

Huawei doesn’t provide charging estimates for SuperCharge, but we were able to fully charge the Mate 20 Pro in around an hour and ten minutes.

Safety measures

Huawei’s Smart Charge protocol, a proprietary part of the SuperCharge spec, identifies the load capacity of the charger and cable and reduces the voltage to match.

In addition, SuperCharge uses specialized components that are “optimized” to handle higher currents, including an 8-layer cooling system and special lining that keeps devices up to 5-degrees Celsius cooler than other fast-charging standards. Huawei says that SuperCharge devices undergo a year’s worth of testing and 10 reliability tests covering everything from short-circuits to extreme temperatures.

The future of fast charging

Fast charging technology is in a constant state of flux, no pun intended. Advancements in integrated circuitry, charge controllers, adapters, and cables could mean smartphones that recharge in minutes rather than hours.

Meizu Super mCharge

Guangdong, China-based smartphone maker Meizu’s promising new standard, Super mCharge, can charge a battery from 0 to 100 percent in 20 minutes. Its 11V/5A charging adapter delivers a whopping 55W of power, and sophisticated circuitry inside Super mCharge-compatible devices prevent the internal temperature from exceeding 102 degrees Fahrenheit. Better yet, Meizu says Super mCharge won’t impact battery longevity — the average 3,000mAh battery will have 80 percent of its capacity available after 800 cycles.

Buy there’s a catch: Super mCharge will require a specific charger, cable, phone, and battery.

Oppo Super Vooc

Oppo Super Vooc, the evolution of Oppo’s Vooc charging technology, can charge a battery even faster than Meizu’s Super mCharge: From 0 to 100 percent in 15 minutes. It uses a low-voltage system that doesn’t produce as much heat as other fast charging standards, and its algorithm regulates the charging current and voltage dynamically to prevent short circuits.

Better yet, Super Vooc doesn’t have Super mCharge’s strict compatibility standards. It requires a custom battery, but it works with Micro USB and USB Type-C chargers.