The charging cable
The USB charging cable is the most abused accessory by any smartphone owner: bent, twisted, pulled, left in the heat and cold. Each of these operations often creates micro-breaks in the cable which, in the long term, considerably reduce its ability to carry electricity to the battery of the device to which the cable is connected. If we want to change the cable and buy one to solve the problem, however, we must pay attention to the quality: a good cable is made of copper, which conducts electricity better than other metals such as aluminum, which are used in cheap USB cables.
The charging source
If the cable is OK, but the smartphone is charging slowly, then we need to look at where the electricity carried by the cable comes from. If the smartphone is connected to a laptop, for example, it is almost certain that it will receive very little power from the USB port. If this is not the case, we risk throwing the computer to charge the phone, or worse, grilling the USB port. If we use Qi standard wireless chargers, charging can be even slower because this standard, although very convenient to use, cannot transfer a lot of energy in a short time.
The charger
If the smartphone is connected to a conventional charger that plugs into a wall outlet, and the charge is very slow, then we must make sure that we are using the most suitable charger for our device. It is not uncommon to have several chargers at home (perhaps inherited from old smartphones) and to use one at random to charge your mobile phone. The problem is that not all chargers are the same: there are more powerful ones and less powerful ones (usually older). From the power depends the charging speed, provided that your smartphone supports the maximum power of the charger.
Smartphone battery
If your smartphone is old, the cause of slow charging is most certainly the battery itself. Over time, the lithium-ion cells that make up batteries degrade, which has two negative effects: the maximum charge the battery can store decreases and charging times increase. The chip that regulates energy entering the battery, to prevent overheating and dangerous electrical discharges, may also begin to have problems with age.
Do not use your smartphone while charging
Finally, the last reason why your smartphone is not charging quickly can be you: if you continue to use your phone while charging, a large part of the energy that enters the battery is immediately used to keep the device on. and active. There's not much you can do: if you need your battery to recharge quickly, you should stop using the device while it's charging.