It seems to be a dead battery because the USB connector seems OK by what you say!
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It seems to be a dead [https://www.ifixit.com/iPhone-Parts/iPhone-4-Replacement-Battery/IF182-000-2|battery] because the USB connector seems OK by what you say!
The iPhone is telling you about it by showing the "powered by outlet" icon even if not charging!
It seems to be a dead battery because the USB connector seems OK by what you say!
The iPhone is telling you about it by keeping the powered by outlet icon even if not charging!