The world’s leading smartphone companies are competing to provide users with a fast charger that can charge the battery faster and in less time, as charging a phone used to take hours but now it is possible to reach a full charge in just minutes.

Despite this significant leap in charging speed, this rapidity comes with a phenomenon most users notice: an increase in the phone’s temperature during charging. This leads some people to wonder if that indicates a malfunction or danger for the battery.

Energy and electronics experts confirm that the rise in the phone’s temperature during fast charging is normal in most cases, as it is a direct result of the process of transferring large amounts of electrical energy and converting them within the device. It is not an indication of a malfunction, as long as the heat remains within the limits set by the manufacturer according to techwhyexplained.

Energy conversion generates heat

The energy journey begins at the power outlet, where the charger converts alternating current to direct current with a higher voltage than what the battery needs. This energy then travels through the cable to the phone.

Inside the device, an electronic circuit known as the power management circuit is responsible for reducing the voltage to the appropriate level for charging the lithium-ion battery, which typically operates at a voltage between 3.7 and 4.4 volts.

Despite significant advancements in the efficiency of these circuits, they cannot convert energy with 100% efficiency; a small portion is lost as heat. The higher the charging capacity, whether 65, 80, or 100 watts, the more heat is lost from this process.

Electrical resistance doubles the heating

Heat is not only produced during voltage conversion but also due to the flow of electrical current through the phone components.

The cable, charging port, electronic circuits, and even the battery itself have natural electrical resistance. When a high current flows during fast charging, a portion of the energy is converted into heat according to Joule's Law, which states that thermal energy increases significantly with increasing current intensity.

For this reason, the phone gets warmer in the initial stages of charging before the charging speed gradually decreases as the battery approaches full capacity.

Battery heat

A complex chemical process takes place inside the battery, as lithium ions move between the electrodes to store energy. When this process occurs too quickly, such as with fast charging, the movement of ions within the electrolyte increases, generating additional heat due to friction and chemical reactions.

Moreover, older batteries or those that have undergone many charge cycles possess higher internal resistance, causing them to heat up significantly more than new batteries when using the same charger.

The phone monitors itself

Manufacturers have equipped phones with multiple temperature sensors that monitor temperatures in various parts of the device to prevent any negative impact on the battery.

When heat approaches safe limits, the phone automatically reduces charging speed and requests the charger to decrease the power sent. This process is known as thermal management.

Many users notice that the phone charges quickly at first, then the process slows down over time or when using applications and games that consume the processor during charging.

Superfast charging

With the emergence of chargers with capacities exceeding 100 watts, companies have turned to developing battery design itself rather than relying on a single cell.

Many flagship smartphones currently use dual-cell batteries, where the energy from the charger is divided between two cells that operate simultaneously. This reduces the current flowing through each cell and minimizes the amount of heat generated while maintaining high charging speeds.

Some devices also rely on technologies such as charging pumps and power distribution systems to enhance efficiency and reduce thermal losses.

When should you be concerned?

Experts say that feeling warmth in the phone during fast charging is normal, but there are signs that indicate stopping use of the charger or seeking maintenance assistance. These include: high temperatures making it difficult to hold the device; repeated warning messages; an unusual smell; and battery swelling.

It is also recommended to use the original charger or certified chargers, avoid covering the phone while charging, place it on a solid surface that allows heat dissipation, and refrain from running heavy games or applications during fast charging. This is because the processor's heat combines with the battery's heat, leading to reduced charging speed or increased stress on device components.

Modern smartphones are designed to handle fast charging, which generates more heat than traditional charging. Therefore, these phones have an integrated system of electronic circuits, sensors, and protection systems, making the increase in temperature a natural part of the power transfer process, rather than an indicator of a problem, as long as the temperatures remain within the limits set by the manufacturer.