Your iPhone stopped charging at 80%. That alone does not mean the battery is bad. Start by reading the charging information in Settings → Battery. The artwork is an educational illustration, not a customer repair or an exact settings screenshot.
Optimized Battery Charging can pause and finish later
This feature reduces the time your iPhone spends fully charged. When it predicts a long charging session, it can delay charging beyond 80% and finish closer to your usual unplugging time. A changed routine can change when it activates. You do not need to disable the feature just because you notice a pause.
Check a selected Charge Limit on iPhone 15 and newer
Go to Settings → Battery → Charging and read your selected limit. Supported models allow a limit between 80% and 100%. A phone stopping near that selected limit may be behaving as intended. It can occasionally charge to 100% even with a lower limit to keep battery charge estimates accurate. On iPhone 14 and earlier, look for Optimized Battery Charging under Battery Health & Charging instead. Menu wording can vary by software version.
Temperature can also slow or pause charging
If the battery gets too warm, the iPhone can limit charging. Move the phone and charger to a cooler location and allow the device to cool normally. A temperature-related pause is different from a selected charging limit. Do not try to force charging through a temperature warning.
Where these checks stop helping
Settings do not repair a damaged charging port, cable or worn battery. If charging remains unreliable under normal conditions, the phone disconnects repeatedly or shuts down unexpectedly, record the symptoms for an evaluation. Do not reset or erase the phone as a test for an 80% charging pause.
Sources and further reading
Common questions
Does stopping at 80% prove my battery is bad?
No. Optimized Battery Charging, a selected Charge Limit or temperature can explain it. The percentage alone does not diagnose battery health.
Should I turn off optimized charging?
Not simply because it pauses. It is designed to reduce time spent fully charged. Read the charging information first.
Related repair help
Get a clear next step.
Call your nearest Phone Repair Guy store or send the device and symptoms for a repair evaluation.