Smartphone charging power: Speed gains, hidden costs revealed

Today, electronics manufacturers are increasingly implementing fast-charging features in devices. This is especially beneficial for devices that require frequent charging, such as smartphones. Many of us are familiar with the scenario where we must leave the house quickly, and the phone's battery is almost dead. In such moments, the fast charging feature proves extremely useful. Below, we explain how charging power affects the charging time of a phone battery.

Smartphones' charging power depends on the technology used and the USB standard. We must look at charging power expressed in watts (W) to understand this process better. Simply put, 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 2.5W, which allowed the battery to be charged in 2-3 hours. However, at that time, the batteries were much smaller.

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

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

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

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

• Power Delivery (from 10W to 100W), developed since 2012
• Qualcomm Quick Charge (up to 27W)
• SuperVOOC (up to 240W) 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. With the same power, a larger battery takes more time to charge fully. The cell's state of charge is also important—manufacturers often provide the time required to charge it from 0 to 100%, from 0 to 50%, or from 1 to 100%.

It's also important to ensure the compatibility of all the charging accessories used. The smartphone does not determine the 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 car, may have limitations.

The element with the lowest maximum charging power limits the charging speed. Sometimes, the smartphone itself decides—if its battery supports charging at 25W, a charger with 50W or 100W won't speed up the charging process; it depends on the weakest link in the charging ecosystem.

Let's move to practical matters. We can use a simple formula to determine how long it will take to charge a battery of a certain capacity: charging time in minutes equals battery capacity (Wh) divided by charging power (W) and multiplied by 60 minutes.

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

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

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

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

As you can see, charging time varies within one manufacturer's range despite similar specifications. The final result is the outcome of many 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 difficult to state whether it shortens battery life. Higher power generates more heat, which can negatively affect components. However, manufacturers ensure that fast charging is safe and should not drastically decrease battery capacity. After years of use, capacity may decrease to about 80%, which still allows for comfortable use of the device. If necessary, replacing the battery is an option and is not very costly.

In conclusion, fast charging is a great convenience, especially in emergencies. When using this technology, ensure you use compatible accessories and know its limitations.