Welcome to Android Central! Had you been noticing poorer battery life recently in the first place? If so, it’s possible that even with the phone plugged in, the power required for the update caused relatively more drain, and if a failing battery can cause the phone to shut off well before it reaches 0%. Unfortunately, since this happened in the middle of an update, it may very well have bricked the phone. Some phones require the battery to be at least 50% before it lets the system update, for this very reason.
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