Understanding the thermal ceiling in portable power

Plug a phone into a modern charger and the first 10 minutes are impressive. The next 20 are not.

This is not a defect. It’s the connected device protecting itself.

As temperature rises during charging, a smartphone’s battery management system reduces the current it will accept, because heat accelerates the chemical degradation that permanently reduces battery capacity.

The charger may be capable of delivering more, but the device simply stops taking it. For anyone building products in the portable power category, this creates an uncomfortable gap between specification and experience.

A device rated at 25 watts is accurate in the sense that it can deliver 25 watts. Whether it delivers 25 watts for the duration of a charge is a different question, and one the specification does not answer.

The specification gap The gap matters commercially because it is invisible at the point of purchase and obvious in use. Consumers compare wattage figures on packaging.

They don’t compare thermal curves, because thermal curves are not published publicly. The result is a category where products differentiate on a number that describes peak output rather than sustained output, and where the actual use

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  Understanding the thermal ceiling in portable power