How Does Fast Charging Work? | Digital Trends

In the increasingly competitive smartphone market, people meticulously examine each and every feature that smartphones have to offer from screen size to processing power before choosing the best smartphone for them.

A relative newcomer to the ranks of sought-after features is fast charging. Technology now allows for a quick charge during the limited downtime we find in our busy day-to-day lives. Who wouldn’t want a smartphone that charges in minutes instead of hours?

If only it were that simple. Charging standards are a complicated mix of chemistry and physics, and each has its own sets of limitations, with incompatibility an issue as well. To make matters worse, smartphone manufacturers tend to slap confusing labels on their charging tech.

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 is everything you need to know about Samsung Adaptive Fast Charging, USB Power Delivery, Qualcomm Quick Charge, OnePlus Warp 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.

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 non-rechargeable 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; 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 types 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).

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 light bulb, 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 usually 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?

USB Power Delivery

The USB Power Delivery (USB-PD) standard was developed by the USB Implementers Forum (USB-IF) and it’s a standard that any manufacturer can use on any device with a USB port. It’s capable of delivering up to 100W, so it’s suitable for use with all kinds of devices beyond smartphones including some laptops, provided they have a USB-C port. USB-PD brings other benefits, too. The direction of the power is not fixed, so you will find portable battery chargers, for example, that have a USB-C port that can be used both to charge another device or to charge the battery pack itself. USB-PD also only provides the power the device needs, so the same USB-PD charger could charge a smartphone at top speed, but then also charge a laptop at its top speed.

Different manufacturers employ the USB-PD standard differently. Here’s how Apple and Google use it, for example.

Apple fast charging via USB-PD

iPhone XS review
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 for many of its phones.

The Apple iPhone 11, iPhone 11 Pro, 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. Intercompatibility 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 hasn’t packed USB-C cables or adapters in iPhone boxes until recently. You’ll also 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%, but stops when it reaches 80%.

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% in 30 minutes using USB-PD.

Google fast charging via USB-PD

Google Pixel 3 and Pixel 3 XL
Julian Chokkattu/Digital Trends
Voltage Current Max Power
USB-PD 9V 2A 18W


  • The same USB-PD kit will work with a number of devices.
  • Google supplies a fast charging charger and cable in the box.


  • The top speeds aren’t quite as fast as some other manufacturers offer.

Every Google Pixel phone from the original to the Pixel 4a is capable of fast wired charging at up to 18W using the USB-PD standard — the same standard Apple is using. It doesn’t require any special chargers or cables.

Supported outputs, cables, and adapters

You can use the charger and cable in the box with your Pixel phone to enjoy maximum charging speeds. If you go for third-party accessories then use any USB-C with USB 2.0 power adapters and cables. If you use a USB-C to USB-A cable, then it will charge your Pixel more slowly, regardless of the power adapter you connect to.

Charging speed

A Pixel phone can charge rapidly from 0% up to around 80% but will slow down beyond that point. You’ll find the same limitations with most phones.

Using the cable and 18W adapter supplied, or any decent third-party one with a similar or higher rating, you can get seven hours of use from a 15-minute charge.

Qualcomm Quick Charge

Simon Hill/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+ 5V/9V (USB-PD), 3.6V – 20V (200mV increments) 3A (USB-PD), 2.5A/4.6A 27W (USB-PD)
Quick Charge 5.0 5V/9V (USB-PD), 3.3V – 20V (200mV increments) 3A/5A/>5A 100W+


  • One of the most widely implemented charging standards.
  • Backward 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-chip technology like the Snapdragon 855, 845, 835, 820, 620, 618, 617, 430, and others, which power phones like the Samsung Galaxy S10, 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. Announced in July 2020, Quick Charge 5 is the latest standard in the series, promising the ability to recharge phones to 50% in five minutes. While support is currently limited to recent phones such as the Samsung Galaxy S20, Quick Charge 4.0+ support is growing in popularity and you can find it in phones like the LG G8 ThinQ, Razer Phone 2, and Xiaomi Mi Mix 3 and it can deliver up to 27W of power. The more widely used 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 that Quick Charge 5 can fully recharge smartphones in 15 minutes, and that the latest version of Quick Charge 4+ can recharge smartphones to 50% in just 15 minutes. The more ubiquitous Quick Charge 3.0 delivers about 50% capacity in half an hour.

In our testing, Quick Charge 4+ took the Razer Phone 2’s big 4,000mAh battery from 18% to 90% in just over an hour.

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 Super Fast Charging and Adaptive Fast Charging

Galaxy S10 Plus
Julian Chokkattu/DIgital Trends
Voltage Current Max Power
Samsung Adaptive Fast Charging 5V/9V 2A 18W
Samsung Super Fast Charging 1.0 11V 2.25A 25W
Samsung Super Fast Charging 2.0 10V 4.5A 45W


  • Built into all Samsung devices.
  • Adaptive Fast Charging compatible with Quick Charge 2.0, Super Fast Charging compatible with USB PD.


  • 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.

Samsung introduced Super Fast Charging with the Samsung Galaxy S10 5G. This phone has a 4,500mAh battery and supports up to 25W charging with the USB Power Delivery 3.0 PPS (Programmable Power Supply) charging standard. The Samsung Galaxy Note 10 Plus hits even higher speeds, using Super Fast Charging 2.0 (as do later models such as the S20 and Note 20). However, to hit the fastest charging it’s capable of requires a special adapter with an unusual 10V and 4.5A rating to output 45W, which means it also requires a 5A cable.

Tech specs and compatible adapters

Samsung’s Adaptive Fast Charging has a theoretical peak of 9V/2A (18W), while Super Fast Charging has a peak of 10V/4.5A (45W). Both standards tend to be a bit more conservative in practice. Tapping into the highest speeds of either requires buying a certified charger, but most Samsung devices support either Quick Charge- or PPS-compatible accessories.

Charging speed

Samsung doesn’t publish charging times for Adaptive Fast Charging or Super Fast Charging. But in our testing, the Galaxy S8, which has a 3,000mAh battery, took about two hours to fully recharge. The Note 10 Plus, meanwhile, took about one hour to fully recharge using the Super Fast Charging standard.

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

Moto G7 TurboPower
Simon Hill/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 3.0.


  • Not as fast as some charging standards.

Motorola’s TurboPower standard, a tweaked version of Quick Charge 3.0, ships on Motorola devices like the Moto G8.

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 Adaptive 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 3.0 (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

how does fast charging work
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
MediaTek Pump Express 4.0 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 coexist — Pump Express 2.0 targets lower-cost Micro USB and USB-C devices, and Pump Express 3.0 targets high-end USB-C phones. The newer Pump Express 4.0 is the same as 3.0, but includes Qi wireless charging support at up to 15W as well.

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. Pump Express 4.0 is also compliant with USB PD 3.0 programmable power supplies, so any USB-PD 3.0 fast charger should work with it.

Charging speed

Pump Express 3.0 or 4.0 devices can charge up to 75% 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 and Warp Charge and Oppo VOOC

OnePlus 6T review
Andy Boxall/Digital Trends
Voltage Current Max Power
Dash Charge 5V 4A 20W
Warp Charge 5V 6A 30W
Oppo VOOC 5V 5A 25W
Oppo Super VOOC 10V 5A 50W


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


Shenzhen, China-based OnePlus licenses Dash Charge and Warp 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. It was rebranded to Warp Charge with the OnePlus 6T McLaren Edition and that’s what you’ll find in the OnePlus 8 Pro, too. Oppo has also developed the much faster Super VOOC, but it’s only available in a handful of phones like the Oppo RX17 Pro.

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 and Warp Charge only work 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 or Warp Charge-compatible wall adapter and charging cord.

Charging speed

OnePlus rates Dash Charge at 60% capacity in 30 minutes. In our testing, the OnePlus 3 charged from 2%to 100% in 1 hour and 14 minutes. We found that Warp Charge took the OnePlus 8 Pro from 0% to 55% in 24 minutes, and charges to 100% in just over an hour.

Oppo claims VOOC-enabled phones can charge to 75% in 30 minutes. When we charged the Super VOOC system with the Oppo RX17 Pro it went from 0% to 40% in just 10 minutes.

Safety measures

Dash and Warp Charge are 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 – 10V 4A/4.5A/5A 40W


  • 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 P40 Pro, Huawei P30 Pro, Huawei Mate 20 Pro, and the Huawei P10. It’s a bit like 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. Older 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. The latest version offers 10V/4A for up to 40W.

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 P40 Pro in around 1 hour and 10 minutes.

Safety measures

The SuperCharge feature, along with Smart Charge, is available on Huawei devices. This unique tool can read whatever charger you’re using and pinpoint its optimal capacity. From there, the tool can modify the charger’s voltage as it needs. 

Producers created SuperCharge with specific design features to carefully control higher currents. Some of those components include an eight-part cooling system and a lining that can keep devices five degrees Celsius cooler than other charging methods. Huawei Supercharge devices are built to last, and they’re thoroughly tested to ensure that products meet rigorous safety and performance standards. The company will test their devices in a year-long trial to observe their products under extreme conditions over time.

The future of fast charging

We know this is the understatement of the year, but technology is rapidly evolving. You can bet that fast charging will soon be the universal standard and will likely slowly replace average chargers over the next several years. Thanks to major growth in integrated circuitry, charge controllers, adapters, and cords, phones could soon potentially recharge over the span of just a few minutes instead of several hours. Early model fast chargers recently gained popularity for their promises to increase your device’s portability and charge quickly. As this technology evolves and becomes more accessible, fast charging will only continue to grow and improve with manufacturing.

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