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

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00:00:04,522 --> 00:00:08,615
Heat and charging schedules
can also slow or pause charging.

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00:00:08,615 --> 00:00:11,940
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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00:00:26,634 --> 00:00:30,354
Current describes how quickly
electric charge flows into it.

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00:00:30,354 --> 00:00:34,165
A higher percentage does not
promise the same charging speed.

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00:00:34,165 --> 00:00:38,283
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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00:00:59,041 --> 00:01:02,039
The controller then holds
voltage near that limit.

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00:01:02,039 --> 00:01:05,350
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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00:01:13,645 --> 00:01:17,555
Eighty percent is not the universal
boundary between these phases.

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00:01:17,555 --> 00:01:22,365
Battery design, temperature, and charging
settings affect the actual curve.

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00:01:22,365 --> 00:01:26,138
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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00:01:34,086 --> 00:01:35,773
On supported iPhones,

29
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Optimized Battery Charging can delay
charging past eighty percent.

30
00:01:40,136 --> 00:01:44,006
It uses learned routines to reduce
time spent fully charged.

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00:01:44,006 --> 00:01:47,492
A selected charge limit can stop
charging near that limit.

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00:01:47,492 --> 00:01:51,342
Temperature controls can also
reduce or interrupt charging.

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00:01:51,342 --> 00:01:55,019
One slow charge cannot
identify which cause applies.

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00:01:55,019 --> 00:01:56,881
Return to the two lines.

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00:01:56,881 --> 00:02:02,111
Near full, controlled voltage and falling
current can explain slower charging.

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00:02:02,111 --> 00:02:06,271
A pause may instead reflect
settings or temperature controls.

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The battery percentage alone
cannot tell those stories apart.