WEBVTT

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Phones often slow charging near full
because their controllers reduce current.

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Heat and charging schedules
can also slow or pause charging.

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Why does phone charging
slow near eighty percent?

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The percentage is a clue,
not a universal switch.

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Watch two lines reveal what
the battery icon hides.

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First, separate the battery
percentage from the charging rate.

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The percentage estimates how
much charge the battery holds.

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Current describes how quickly
electric charge flows into it.

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A higher percentage does not
promise the same charging speed.

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Our diagram shows a simplified
lithium-ion charging cycle.

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It is not a measurement
from a particular phone.

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During the main charging phase,

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the controller can hold
current roughly steady.

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Meanwhile, the battery voltage rises.

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Voltage is the electrical difference
across the battery's terminals.

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The controller monitors both quantities.

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Eventually, the voltage reaches
the charging limit for that battery.

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The controller then holds
voltage near that limit.

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Current gradually falls
while charging continues.

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This is why the last part can take longer.

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The same charger remains
connected throughout.

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The controller changes
how the battery charges.

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Eighty percent is not the universal
boundary between these phases.

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Battery design, temperature, and charging
settings affect the actual curve.

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Modern phones may use more
complicated charging profiles.

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This drawing explains the relationship,
not every implementation.

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A gradual slowdown also
differs from a scheduled pause.

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On supported iPhones,

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Optimized Battery Charging can delay
charging past eighty percent.

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It uses learned routines to reduce
time spent fully charged.

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A selected charge limit can stop
charging near that limit.

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Temperature controls can also
reduce or interrupt charging.

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One slow charge cannot
identify which cause applies.

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Return to the two lines.

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Near full, controlled voltage and falling
current can explain slower charging.

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A pause may instead reflect
settings or temperature controls.

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The battery percentage alone
cannot tell those stories apart.