Why is my smartphone charging slowly?

​The short answer is that it could be due to a cable, charging adapter, and/or an incompatible fast charging protocol. Let's take a closer look at each of these factors.

​

Situation: Your smartphone supports fast charging, but when connected to a charger, it charges slowly. Here are a few reasons for this unpleasant situation.

Reason1. The charger and/or cable is defective.

Try connecting using the same cable and the charger to another smartphone that supports fast charging. Will fast charging turn on? If not, replace the cable and try again. If charging appears, it's obviously the cable and it needs to be replaced. If fast charging doesn't work again, then either the charger is defective, or it doesn't support fast charging at all, or it doesn't support fast charging protocol compatible with your smartphone (see next point below).

Conclusion: To buy a new quality USB charger.

Reason2. Your charger does not support fast charging or does not support the fast charging standard compatible with your smartphone.

• To check the charger's ability to provide fast charging, look at its specifications (alternatively, look at the product description on the online store page) or look for the markings on the charger's housing. The housing should list the charge output parameters, for example like this: 5V,9V,12V,15V,20V - 5A or 3.3-11V 3A. There may also be other formats to describe the charging support for different voltages and maximum amperage. Sometimes you can find there abbreviations of supported fast charging standards, e.g. PD(PDO), QC, PPS, VOOC, HyperCharge, etc. You can familiarize yourself with the variety of fast charging standards on this page.

• If there is a marking indicating fast charging (or on the product page in the e-shop), then perhaps the fast charging standard is not compatible with your smartphone. This situation may occur with some proprietary charging standards such as VOOC, Hypercharge, etc. which are most commonly implemented in Chinese smartphones. Proprietary standards are extremely rare, almost never found in third-party chargers or competitor devices (OnePlus vs Xiaomi vs VIVO vs iQOO). However, modern Chinese smartphones often support in addition to their own proprietary standard of fast charging several universal ones, such as PD (Power Delivery) and QC (Quick Charge), but the charging speed will be much slower than its own proprietary standard. For example instead of 120W, the charge will be limited to 27W max. 

• Note that if you own a Chinese smartphone (Vivo, iQOO, OnePlus, OPPO, Xiaomi, etc.), it is often important to use not only the charger of the same manufacturer, but also the cable, because such cables have a special chip inside, and often modified contact pads capable of withstanding high current during charging (above 5Ampere).

• ​Some old USB chargers do not support fast charging standards and can provide DCP standard charging with a maximum of 7.5W only.

• Some cheap noname cables do not have wires that connect to the pins that are used to “communicate” between the charger and smartphone to set a compatible fast charging protocol and its power. In this situation, you need to change the cable to a better one.

• Conclusion: If the problem is in the compatibility of the smartphone with the charger, or in the lack of fast charging protocols on the side of the charger adapter, then you need to buy a compatible or universal charger that supports PD, QC and preferably PPS standards. If there is no original USB cable for the original proprietary charger - you need to buy a new original cable.

Reason3. Charging is fast at first glance, but not fast enough.

• The reason for insufficiently fast charging may be in the cable. For example, to charge some Samsung smartphones as fast as possible, it is necessary to use UsbC-UsbC cables with a maximum power of 100W or 240W because these cables are designed to handle a current of 5Amp and have an e-maker chip that tells the charger to activate a more powerful charging mode, even if the actual charge will have a maximum power of 45W.

• ​Another reason could be a charger that does not have the right charging protocol (e.g. PPS of the right range) and switches to a slower type of fast charging, or the power is too low. It is important to realize that even if at first glance the charging adapter says 45W, it does not always mean that you will be able to fully utilize the available 45W as this level of charge can be achieved with a certain protocol with a certain voltage, for example 20V 2.25A which your smartphone might not be able to accept and therefore activates a lower voltage and lower charging power.

• ​Another reason is overheating of the charger. The conversion of energy from household alternating current (AC) to direct current (DC) is accompanied by unavoidable losses of 5-10% at best, sometimes even up to 20%. Energy losses are expressed in the heating of the adapter and if the charging adapter works at full power, its size is compact and the adapter has a lightweight (which means that it does not have enough heat sinks), leads to its overheating, which not only further deteriorates the efficiency factor further increasing losses, but also to unstable operation of the adapter itself, up to the failure of its internal components.

• ​Simultaneous charging of several devices from one charger. Some chargers have several connection ports for charging devices. Different manufacturers realize power distribution between the ports in different ways. And even if the charger is claimed to be fast and it charges quickly using one of the available ports, it may turn out (true for some very cheap noname chargers) that when several charging devices are connected simultaneously, the charger switches to DCP protocol and gives a maximum of 7.5W to each USB output. Another unpleasant situation can be observed when connecting a second device causes a short-term power supply break to all connected devices, which can cause e.g. rebooting of devices without their own battery. However, there are chargers that do not interrupt the power supply in the described situation, such as the SlimQ 3C1A 150W. 

Conclusion: When buying a charger, try to choose a more powerful charger approx. 20-30% more powerful than your device needs (especially important for laptops) e.g. 65W if you need 45W, 140W if you need 100W. This choice will not only allow you to activate better, more advanced and powerful charging protocols, but will also prolong the life of your charger. 

P.S. To figure out what is happening while charging your smartphone or laptop via USB cable you can use a USB tester such as Power-Z KM003C, such a tester will determine the type of fast charging, which is turned on during charging, do cables testing and chargers, but it is an expensive device. An alternative is this compact and affordable HiDANCE HDC-085C tester, it only shows the power, current and voltage flowing through the USB cable, which can help at least in determining how much power your device is being charged with.