Understanding fast charging: What powers your smartphone battery?

Electronic equipment manufacturers are increasingly equipping their devices with fast-charging features. This is especially useful for devices we charge frequently and even daily. Smartphones are a perfect example. Many of us have probably found ourselves in the following situation: we must leave home in a few minutes, only to realize that the battery is almost empty. This is when we most appreciate the benefits of fast charging. However, it is worth knowing how power affects phone battery charging time. You will find the answer below.

The charging power of a smartphone depends on the technology and USB standard used. To understand this better, we must first know the charging power expressed in watts (W). In short, this parameter determines how much electrical energy we can transfer to the receiver. We almost always talk about charging via a USB cable when charging smartphones. Early standards offered a charging power of 2.5W, which allowed for charging the battery in 2-3 hours. However, it is worth remembering that battery sizes were much smaller before the smartphone era.

With the introduction of the USB 3.0 standard, charging power increased to 4.5W. Currently, even basic USB chargers are faster, offering a voltage of 5V and a current of 2A, which gives a charging power of 10W. Although it is not an impressive value, it isn't easy to find a smartphone today that does not offer at least this charging power.

USB Type-C cables can transfer more power thanks to a current of 3A (at a voltage of 5V, this gives a charging power of 15W). Higher power requires fast charging technology. We can talk about fast-charging technology even in smartphones with a maximum power of 18, 20, or 25W (for example, the flagship Samsung Galaxy S24).

Looking at the latest smartphones, charging power often amounts to 45, 67, 80, or over 100W. The record holders can boast charging power exceeding 200W. Faster charging, however, requires more energy, which, in theory, is simple to achieve. The problem is that this is accompanied by an increase in temperature, which generates large amounts of heat. As a result, this can lead to faster battery wear or device damage.

Several fast-charging technologies are available on the market, which, thanks to appropriate protocols and optimization of current parameters, allow for the safe charging of a high-power battery. The most popular are:

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

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

Charging power is crucial for determining how long we will wait for the battery to charge. Another critical parameter is battery capacity. A larger battery may take longer to charge at the same power. The battery discharge level is also significant – manufacturers often provide charging times from 0 to 100%, 0 to 50%, or 1 to 100%.

Additionally, paying attention to the compatibility of all charging accessories is essential. Therefore, the smartphone must not only support a given charging power but also the charger plugged into the network and the cable. The source from which we charge the phone is also essential – a power bank, laptop, car USB socket, or other device may have some limitations.

The element that supports the lowest maximum charging power determines the phone's charging speed. Sometimes, this is our smartphone – if the battery supports charging with a power of 25W, connecting it to a 50W or 100W charger will not shorten the charging time. Therefore, the charging time depends on the weakest element in the charging set.

Let's move from theory to practice. You can use a simple mathematical formula to calculate how long it will take to charge a battery with a specific capacity. The theoretical formula for calculating battery charging time from 0 to 100% is: charging time in minutes equals battery capacity (Wh) divided by charging power (W) multiplied by 60 minutes.

For these calculations, you can assume that the battery capacity is 5000mAh (5000mAh gives about 19Wh at a voltage of 3.7V), which is standard in smartphones today. The results of these calculations for several typical charging powers with a battery capacity of 5000mAh will look as follows:

• at 18W charging - about 62 minutes
• at 25W charging - 45 minutes
• at 33W charging - 34 minutes
• at 45W charging - 25 minutes
• at 67W charging - 17 minutes
• at 80W charging - 14 minutes
• at 120W charging - just over 9 minutes
• at 240W charging - 5 minutes

The above results look impressive at higher powers. Unfortunately, in practice, the battery charging time is longer. Even with compatible devices and accessories, it is not possible to achieve maximum charging power all the time. There are power losses, and the software and safety measures in the charger may limit power due to rising temperatures.

It is worth checking the manufacturers' declarations to obtain more realistic results. For example, the Xiaomi Redmi Note 9 (5000mAh battery, 18W charging) charges from 0 to 100% in 153 minutes, while the Xiaomi Redmi Note 11 (5000mAh, 33W) charges in 60 minutes. Models with 67W charging power, like the Xiaomi Redmi Note 12 Pro, need about 46 minutes. The fastest models, like the Xiaomi Redmi Note 13 Pro+ with 120W charging, charge to full in 19 minutes.

Even smartphones from the same manufacturer have different charging times despite similar specifications. The final results depend on many factors, including charging technology, battery capacity, and the components' efficiency.

The final issue to be aware of is the impact of fast charging on battery lifespan. It is difficult to say whether faster charging shortens battery lifespan unequivocally. More power generates more heat, which can negatively affect the components. However, manufacturers ensure that quick charging is safe and does not cause a significant decrease in battery capacity. After 3-4 years of use, the capacity may drop to about 80%, which still allows for comfortable phone use. The battery can be replaced if necessary, which is not very expensive.

In summary, fast charging is a big convenience, especially in emergencies. However, it is essential to use compatible accessories and be aware of this technology's limitations.