Understanding the thermal ceiling in portable power

When you plug a phone into a modern charger, the first 10 minutes of charging feel fast, but the next 20 minutes slow down significantly.

This isn't a flaw in the charger or phone.

Instead, it's a safety feature.

As the phone charges, its battery management system (a built-in computer that controls charging to protect the battery) detects rising temperatures.

Heat speeds up the chemical breakdown inside the battery, which permanently reduces its capacity over time.

To prevent this, the system gradually reduces the amount of power the phone accepts, even if the charger could provide more.

The charger may be rated at 25 watts, meaning it can deliver that much power, but the phone won't always take the full amount due to thermal limits.