iPhone 17 battery percentage increases after restart

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Level 1

4 points

iPhone 17 battery percentage increases after restart

Hi everyone,

I’m noticing a strange issue with my battery percentage reading. If I charge my iPhone 17 around 80% and then restart it, the battery percentage immediately increases to around 83% or 84% as soon as the phone boots back up. This happens consistently.

Since this is a brand new iPhone 17 running iOS 20, my Maximum Battery Health is still at 100%.

Is this a known software calibration bug, or is it a sign that my physical battery is beginning to degrade?

Posted on Aug 29, 2026 10:49 PM

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Answer 1

Aug 30, 2026 2:09 AM in response to LD150

An iPhone does not directly “measure percent full” like a fuel gauge. It estimates usable charge from battery voltage, current flow, temperature, load history, and an internal battery management model.

Around 80%, especially if you use an 80% Charge Limit, the estimate can be slightly conservative while the phone is charging or has just been unplugged. During a restart, iOS reloads the battery management data and may perform a fresh estimate under a different load condition. That can add an additional few percentage points that were physically present but not reflected in the prior display.

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Answer 2

LD150

Level 10

105,530 points

Aug 29, 2026 11:46 PM in response to Aryan_23

Charge% and health% are estimates.

Charge it to 100% every night using optimised charging and it will settle.

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