My older iPhone already needs a battery replacement, but I'm trying to understand what might be causing this specific problem. When the battery reaches 19% or lower, plugging it in doesn't make it charge unless I restart the phone. I also left it connected overnight at around 20%, but it failed to charge and dropped to 18% by morning. It's an iPhone 11 running iOS 26.6, and the battery's maximum capacity is 71%.
1 Answer
A maximum capacity of 71% is severely degraded, so the battery is the most likely culprit. An aging battery can report its charge level inaccurately, shut down charging unexpectedly, or lose power even while connected. Still, try a different reliable cable and power adapter, and check the charging port for lint or debris. If the problem continues after those checks, replacing the battery is the practical fix. If a new battery doesn’t solve it, the charging port or charging circuitry may need inspection.

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