New answers tagged samsung
Galaxy S3 is not officially supported by Ubuntu touch but, there is a ROM available you can flash via clockworkmod. i9300 Ubuntu wiki i9300 Ubuntu XDA Rom download link However, this ROM is discontinued since 2013, and according to the XDA page: "No GSM/Phone calls". So, try at your own risk.
Maybe an end of life battery? Check in the Bios (under boot options) if there is: Smart Battery Calibration entry, then run it! So restart and check the accuracy of the battery level, you can access it clicking the energy panel icon (the battery icon top right on the panel).
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