Unpacking the power dynamics of smartphone fast charging

These days, electronics manufacturers are increasingly incorporating fast charging features in devices. This is particularly useful for devices that require frequent charging, such as smartphones. Many of us are familiar with the situation where we need to leave the house quickly, and the phone's battery is nearly dead. In such moments, the fast-charging feature is incredibly useful. Below, we explain how charging power affects the charging time of a phone battery.

The charging power of smartphones depends on the technology used and the USB standard. To better understand this process, we need to consider charging power expressed in watts (W). Put simply, it is the energy we can deliver to the device.

Smartphones are most often charged via a USB cable. Initial standards predicted a charging power of 2.5 W, which allowed the battery to be charged in 2-3 hours. However, back then, the batteries were much smaller.

The introduction of the USB 3.0 standard increased charging power to 4.5 W. Currently, even basic USB chargers offer a charging power of 10 W, providing a voltage of 5 V and a current of 2 A. Today, finding a smartphone that can't charge with such power is hard.

USB Type-C cables boost the charging capability to 15 W, thanks to a current of 3 A (at 5 V voltage). With increased power, fast charging technology becomes necessary. Even smartphones with a maximum charging power of 18, 20, or 25 W (like the Samsung Galaxy S24) rely on fast charging technology.

The most advanced smartphones offer charging power of 45, 67, 80, or sometimes over 100 W. Some models even exceed 200 W. However, as power increases, so does the temperature, which can lead to faster wear or damage to the device.

Different fast charging technologies ensure safe charging at high power by using advanced protocols and optimizing current parameters. The most popular systems include:

• Power Delivery (from 10 to 100 W), developed since 2012
• Qualcomm Quick Charge (up to 27 W)
• SuperVOOC (up to 240 W) used by brands such as Oppo, OnePlus, realme, Vivo
• Huawei SuperCharge
• MediaTek Pump Express

It is also possible to combine different technologies to increase total charging power.

Charging power is crucial for estimating how quickly we can charge the battery. However, we must also consider other factors, such as battery capacity—a larger battery takes more time to fully charge with the same power. The cell's charge state is also important—manufacturers often provide the time required to charge from 0 to 100%, from 0 to 50%, or from 1 to 100%.

The compatibility of all the charging accessories used is also critical. It's not just the smartphone that affects charging speed; the charger and cable must also support the required charging power. It's also worth noting that the power source, such as a power bank, laptop, or USB port in a vehicle, may have its own limitations.

The charging speed is limited by the component with the lowest maximum charging power. Sometimes it's the smartphone itself that sets the pace—if its battery supports charging at 25 W, a charger with 50 W or 100 W won't speed up the process. It's all about the weakest link in the charging setup.

Let's put it into practice. To determine how long it will take to charge a battery of a certain capacity, we can use a simple formula: charging time in minutes equals battery capacity (Wh) divided by charging power (W) and multiplied by 60 minutes.

For instance, assuming a battery capacity of 5000 mAh (which at a voltage of 3.7 V gives 18.5 Wh), the results for different charging powers will look as follows:

• 18 W - about 62 minutes
• 25 W - 45 minutes
• 33 W - 33 minutes
• 45 W - 25 minutes
• 67 W - 17 minutes
• 80 W - 14 minutes
• 120 W - just over 9 minutes
• 240 W - 5 minutes

These values show impressive charging times at higher powers. In practice, charging can take longer, even with fully compatible devices and accessories. Power losses or limitations due to increased temperature can affect charging time.

To obtain more realistic results, it's advisable to consider the manufacturer's data. For example, the Xiaomi Redmi Note 9 (5000 mAh battery, 18 W charging) takes 153 minutes to charge from 0 to 100%, while the Xiaomi Redmi Note 11 (5000 mAh, 33 W) takes 60 minutes. Models using 67 W power, like the Xiaomi Redmi Note 12 Pro, take about 46 minutes. The fastest models, such as the Xiaomi Redmi Note 13 Pro+ with 120 W charging, reach full charge in 19 minutes.

As you can see, charging time varies even within one manufacturer's range, despite similar specifications. The final outcome results from several factors, such as the charging technology used, battery capacity, and the quality of components.

It's also worth considering how fast charging affects battery life. It's challenging to clearly state whether it shortens battery life. Higher power generates more heat, which can negatively affect components. However, manufacturers assure that fast charging is safe and should not drastically decrease battery capacity. After years of use, capacity may reduce to about 80%, which still allows for comfortable use of the device. If necessary, replacing the battery is an option and isn't very costly.

In conclusion, fast charging is a significant convenience, especially in emergencies. When using this technology, ensure compatible accessories and be mindful of its limitations.