Battery level frozen at 19%

Hi all, I’ve installed flyme
After an unexpected shut down the battery level got frozen at 19%, no mater what I do, restart, charge all the night, total discharge, battery level is always 19%.
I haven´t got root access (this firmware version doesn´t have the easy way to do it) thus I can’t use recalibration tools.
The worst, I can’t reinstall firmware because battery level is under 20%
Any sugestions?
Thanks in advance

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