Fast charging at 45W, 67W, and 120W: why more watts don’t always mean faster phone charging

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

Fast charging has made a grand entrance with batteries that support very high figures. But before choosing a phone, especially if this parameter appeals to you, it’s worth bearing in mind that more isn’t always better and that there is an ideal middle ground.

The technology behind fast charging

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

Nowadays we can find phones that charge at 45W, 67W and even 120W or more (although we’ll focus on the typical market ranges rather than the absolute extremes), and the higher the figure… does that mean better? Not entirely: the phone will indeed charge faster, but there are certain issues that arise when ramping up fast charging, such as heat.

Moreover, just because a battery supports 120W fast charging does not mean it will recharge in half the time of a 60W one. It doesn’t work that way; as the numbers rise, the time saved becomes smaller because batteries have physical limits.

The limits of fast charging

Batteries have limits that cause fast-charging values to “stall”:

• A battery that supports 120W fast charging will not always charge at 120W. The power is maximum at the start of charging, and it gradually reduces from about 50–80% to protect the cells. This is easy to observe on a charger with a display that shows the real-time power being supplied (I use Anker Prime for this).
• Fast charging generates heat, and the higher the power, the higher the temperature. If the phone reaches too high a temperature, it will automatically reduce charging power to prevent damage.
• Although batteries have durability protection systems, subjecting them to constant stress with very powerful fast charging can reduce their total capacity to retain a charge over time. In other words, over time they won’t fully recharge.

Where the numbers stop mattering

Although there are nuances with silicon-carbon batteries that push beyond 8,000 mAh, and obviously these take longer to recharge, the ideal balance right now sits in a range of 65 to 80W. With this charging power you can have your phone recharged in roughly 30 to 40 minutes without generating too much heat.

If you glance at the table above, moving from 25W to 45W (a 20W difference) saves roughly a quarter of an hour charging the phone. A similar effect occurs when moving from 45W to 67W (a 22W difference) because the gain is a quarter of an hour. However, moving from 67W to 120W (a 53W difference) results in the same 15 minutes.

With this we mean that going from 67W to 120W (almost doubling the power) only saves the same 15 minutes as in the earlier steps, but with significantly more heat generated. Efficiency, therefore, is reduced.

Which phones have good fast charging?

Fast charging hasn’t arrived equally across brands. Some have been delivering strong numbers for years in their devices, while others have gradually embraced them. In any case, today there are solid options if you value fast charging:

• Samsung Galaxy S26 Ultra. It took a while, but with the Samsung Galaxy S26 Ultra we’ve seen the highest fast charging within the brand: 60W. It sits slightly below the ideal range we mentioned, but it’s still a strong figure if you want your phone charged quickly, especially considering its 5,000 mAh battery.

• Xiaomi 15T. As we’ve seen in the previous generation, the Xiaomi 15T repeats 67W fast charging in a battery that has grown only slightly compared to its predecessor (5,500 vs 5,000 mAh). You’ll also be able to have it fully recharged in a very short time.

• Oppo Reno14 5G. If you’re looking for a little extra within the ideal range, the Oppo Reno14 5G packs a solid 6,000 mAh battery that supports 80W fast charging. It can reach higher power and will charge to 100% in around 40 minutes.

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