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One of the biggest smartphone buzzwords in recent years is fast charging. You hear it everywhere and smartphone companies boast about how fast their latest devices can charge.

It’s crazy to think that a few decades ago it would take you an entire night to fully charge your phone, and now it can be done in less than 30 minutes. That’s all thanks to fast charging.

But what exactly is fast charging, and how does it work? Is it safe for your battery? Let’s find out.

What is fast charging?

Fast charging is a battery charging technology that decreases the time it takes to charge a smartphone battery to full capacity by increasing the amount of power that is sent from the charger to the battery. A basic USB charger can output around 2.5W of power. In comparison, some fast chargers can output upwards of 100W.

Qualcomm’s Quick Charge is the dominant fast charging technology used in most smartphones, However, there are other fast charging standards that exist such as USB Power Delivery (PD). Some manufacturers even have their own brand-name fast charging technology.

But not all smartphones support fast charging. For a phone to be able to fast charge, it needs to have a charging circuit that’s designed to regulate the high amounts of power required for fast charging.

And even if a smartphone supports fast charging, it needs a charger and cable that match its fast-charging standards for it to be effective. Using a different fast charging standard to that of your phone will not work.

How does fast charging work?

To understand how fast charging works, you first need to understand the basics. There are three words (and letters) you need to know: amps (A), volts (V), and watts (W).

  • Amps (A): The current or amount of electricity flowing to the battery.
  • Volts (V): The strength of the current flowing to the battery
  • Watts (W): The total power output (Amps x Volts = Watts)


To make better sense of this, think of a watering hose. Amperage (A) can be likened to the width of the hose, which determines how much water can come out of the hose at any given time. Voltage (V) can be likened to the water pressure, which determines how fast the water flows through the hose and how strong that flow is. And wattage (W) can be compared to the amount of water coming out of the hose.



The higher the voltage and amperage, the higher the wattage. A 12V/3A charger has a wattage of 36W, which is higher than the 15W of a 5V/3A charger. The higher the watts, the faster the charge.

The fast charging process

Smartphone batteries charge in two phases. Fast charging takes advantage of the first phase to increase the flow of power to the battery to shorten the charge time.


Battery charging occurs in two phases: constant current+rising voltage and constant voltage+falling current. The first phase is where the fastest charging takes place.

Phase 1: Constant Current/Increasing Voltage

In this phase, the current (A) of the battery is constant and at its highest. On the other hand, the voltage (V) starts off low and increases over time until it reaches its peak.


Phase 2: Constant Voltage/Decreasing Current

Once the voltage increases to its maximum, it stops there and remains constant. The current, however, begins to drop. At this point, the charging speed slows down.


A high voltage causes heat, which is not good for the battery. But because the voltage is low in the first phase of charging, fast chargers are designed to take advantage of this low-voltage window and pump as much current as possible into the battery before it reaches peak voltage.

That means that fast charging is most effective during the first phase of the charging cycle. Therefore, fast charging works best when the battery is below 50%.

This is why when smartphone manufacturers advertise the charging speed of their devices, they often mention the time it takes for the battery to reach 40%, 50%, or 60% full. And if they do mention how long it takes to reach 100% capacity, you will notice that it takes considerably longer to charge from 50% to 100% than it does to charge from 0% to 50%. That’s because of the charging phases and the fact that fast charging happens mostly in the first phase.

Because constant high voltages can be detrimental to battery life, the amount of voltage and current passed to the battery is controlled by a charge controller circuit inside the phone. This device is equipped with voltage and heat sensors in order to regulate the amount of power and keep the battery and the charger safe from damage.

What do you need for fast charging?

For fast charging to work, you need to make sure you have the following:


fast charger adaptor

For fast charging to work, you need a fast charger. A low output charger will charge slowly, whereas a high output charger will charge faster. Plain and simple. To know what the output of a charger is, just read the writing on the adaptor.

For example, if it says the output is 5V 3A, it means it has a total output of 15W (W=V x A).


The type of cable and USB connector used can have an impact on the charging speed, too. A USB 1.0 and USB 2.0 plug can deliver 2.5W of power, which is the typical charging rate of a normal, slow-charging phone. USB 3.0 can deliver 4.5W of power, whereas USB-C plugs that use the USB 3.1 spec can output up to 100W.

Compatible smartphone

If your phone doesn’t have fast charging technology, then it can’t support it. Even if you have a fast charger with the right cable, a non-fast charging phone will continue to charge at normal speed.

To know the maximum charging speed a phone can support, you just need to have a look at its battery and charging specifications.

Fast charging standards

When it comes to fast charging, not all chargers are the same. There are many different fast-charging standards out there. The two most dominant standards are Qualcomm Quick Charge and USB Power Delivery (USB PD). Most of all the other fast charging standards that exist are offshoots of these two standards.

Qualcomm Quick Charge

Qualcomm Quick Charge is perhaps the most popular fast-charging standard in the world. This is probably thanks in part to the presence of Qualcomm’s Snapdragon processors in a large number of smartphones. However, not all smartphones that have a Snapdragon processor support fast charging.

Qualcomm has four different backwards-compatible versions of the Quick Charge standard.

QC version Voltage Current Max. Output Compatibility
Quick Charge 1.0 5V 2A 10W  
Quick Charge 2.0 5V/9V/12V 1.67A/2A/3A 18W QC 1.0
Quick Charge 3.0 3.6V-22V 2.5A/4.6A 36W QC 2.0
Quick Charge 4.0 3.6V-20V 2.6A/4.6A 100W QC 3.0
Quick Charge 4.0 (USB PD) 5V/9V 3A 27W QC 3.0/USB PD
Quick Charge 4.0+ 3V-21V 3A 27W QC 3.0/USB PD

Other fast charging standards that based their technology on Qualcomm Quick Charge include Samsung Adaptive Fast Charging, Motorola TurboPower 15+, and Huawei SuperCharge 2.0.

USB Power Delivery

USB PD is a fast charging standard that you can find on smartphones as well as a whole bunch of other devices because USB ports are basically everywhere. Using the necessary circuitry and software, USB Power Delivery augments the basic USB charging speed for up to 100W of output power.

Of course, 100W of power is too much for smartphones but perfectly fine for charging laptops and other high power devices. Smartphone fast chargers that use USB PD tend to have an output of between 7.5W and 30W. However, some mobile chargers can provide even more power than that.

Apple’s fast charging standard, Apple Fast Charging, is based on USB PD, as is Samsung Super Fast Charging 2.0.

Other fast charging standards

There are other fast charging standards out there such as the OnePlus WarpCharge and Oppo’s Super VOOC. Interestingly, Oppo’s VOOC technology is developed by them (not based on QC or USB PD) and is licensed to OnePlus to use in their fast charging technology.

MediaTek, the company that makes smartphone processors, also has a fast charging standard called MediaTek Pump Express 4.0.

Fast charging standard comparison

Charging Technology

Base standard



Total Power

Samsung Adaptive Fast Charger

Qualcomm QC 2.0




Samsung Super Fast Charging 2.0





Oppo Super VOOC 2.0





OnePlus Fast Charge





OnePlus WarpCharge 30





Huawei SuperCharge 2.0

Qualcomm QC




MediaTek PumpExpress 4.0

USB PD 3.0




Motorola TurboPower 15+

Qualcomm QC 3.0




Motorola TurboPower

USB PD 2.0




How does wireless fast charging work?

Wireless charging is a modern way of charging smartphones using a process known as electromagnetic induction. Inside a wireless charger is a copper transmitter coil, whereas inside a smartphone is a receiver coil. When you place a phone on a wireless charger, power is transferred from the charger to the phone.



With wireless fast charging, the charging pad transfers more power to your phone while charging. But for it to work, you need fast charging adaptor and cable, just as with standard wall fast-charging. The more power is transferred to the phone from the charger, the less time it will take to charge.

Wireless fast charging is also most effective when the battery is almost empty. The charging speed decreases as your battery gets full to avoid damaging it.

Unlike wall fast charging, wireless fast charging does not have many different standards. Most wireless chargers are Qi (pronounced “chee”) compatible, which is pretty much the universal standard. That means you can charge your iPhone on the same wireless fast charger on which you’d charge a Galaxy Watch.

Can fast charging damage a phone’s battery?

Under normal circumstances, fast charging should do no major damage to a phone’s battery because it’s not the speed of charging that degrades the battery. What can be damaging is the heat that builds up during charging. But thanks to the two-phase charging process explained earlier, fast chargers are able to avoid overheating the battery.

Remember, smartphone batteries are in a constant state of decay, whether they’re used or not. It’s just the way they are. Any negative impact fast charging would have on your battery would be negligible in the greater scheme of things. The only way a fast charger can critically damage a battery is if it malfunctions.


Fast charging is god-sent in this fast-paced world we live in. Smartphone batteries are getting larger in capacity, and nobody wants to wait forever for their phone to charge. And thanks to the way the technology is designed, there is no need to worry about fast charging damaging your phone’s battery.

Just remember, for fast charging to work on your phone, it must be compatible with fast charging and you have to use the correct charger. Otherwise, fast charging won’t work.

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