Why more watts does not always mean charging your phone sooner

Depending on the mobile phone we have, we can have its battery fully recharged in approximately an hour or a matter of minutes. But… why does this happen? Why don’t all batteries take the same time to recharge and what should we take into account when buying a mobile phone?

Fast charging has arrived in style with batteries that support very high figures. But before choosing a mobile phone, especially if this parameter is attractive to us, we should keep in mind that more is not always better and that there is an ideal intermediate point.

Fast charging technology

Fast charging increases the electrical power sent from the charger to the phone, thereby reducing the time needed to complete the charge. It does this by increasing the watts (W) sent from the charger to the phone through the cable.

Nowadays we can find mobile phones that charge at 45W, 67W and even 120W or more (although we will focus on the usual ranges on the market and not on the absolute ones), and the higher the figure… The better? Well, not completely: the phone will charge in less time, but There are certain problems that arise from increasing fast chargingas is the case with heat.

Furthermore, just because a battery supports 120W fast charging does not mean that it recharges in half the time of a 60W battery. This doesn’t work like that; As the numbers go up, the time we gain is less and less because batteries have physical limits.

The limits of fast charging

Batteries have limits that cause fast charging values ​​to “stagnate”:

• A battery that supports 120W fast charging does not always charge at 120W. The power is maximum at the beginning of charging, and is progressively reduced from 50-80% to protect the cells. We can see this well in a charger with a screen that shows the power it supplies in real time (I use in Anker Prime for this).
• Fast charging generates heat and the higher the power, the more the temperature will rise. If the phone reaches too high a temperature, it will automatically reduce the charging power to prevent damage.
• Although batteries have systems in place to protect durability, subjecting them to constant stress with very powerful fast charges can reduce their overall ability to retain a charge over time. That is, over time they will not fully recharge.

At what point do numbers stop mattering?

Although there are nuances due to the arrival of the silicon-carbon batteries with figures that even exceed 8,000 mAh, and obviously these take longer to recharge, The ideal balance right now is in a range of 65 to 80W. With this charging power you can have your mobile recharged in approximately 30 or 40 minutes without generating too much heat.

If you take a look at the table above, going from 25W to 45W (difference of 20W) saves us approximately a quarter of an hour charging the mobile. Something similar happens if we go from 45W to 67W (difference of 22W) because the difference is a quarter of an hour. On the other hand, if we go from 67W to 120W (difference of 53W) the time is the same, 15 minutes.

With this we want to reflect that going from 67W to 120W (almost double the power) only saves the same 15 minutes that we gained in the previous jumps, with much more heat generated. Efficiency is therefore reduced.

What phones have a good fast charge?

Fast charging has not arrived in all brands equally. Some have been implementing good figures on their mobile phones for years and others have been embracing them little by little. In any case, today we can find good purchase options if you value a good fast charge:

• Samsung Galaxy S26 Ultra. It took a while, but with the Samsung Galaxy S26 Ultra We have seen the highest fast charging within the brand: 60W. It is slightly below the ideal range that we have mentioned, but it is still a good figure if you want to have your phone recharged in a short time, especially considering that its battery is 5,000 mAh.

• Xiaomi 15T. As we have been seeing in the previous generation, the Xiaomi 15T It repeats the 67W of fast charging in a battery that has grown little compared to its previous generation (5,500 versus 5,000 mAh). You can also have it fully recharged in a very short time.

• Oppo Reno14 5G. If you are looking for a little extra within the ideal range, the Oppo Reno14 5G It incorporates a good 6,000 mAh battery that supports 80W fast charging. It will be able to reach greater power and will be charged to 100% in around 40 minutes.

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Images | Ivan Linares (edited), Samuel Fernandez in Xataka Mobile

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