@SlionSadly all too true in general...
However... 😃 !!! I FIXED IT !!! 😃
Disassembly was easy with guide referenced above on github. Actually impressed by how repairable this phone is.
Removed battery (cell), did the "prick a hole in the cell to release the gas" trick (don't try this at home - see below). Put it back together and my phone is working just fine after 4 hours' careful work. Will be ordering a new battery from Indiegogo.
Obviously, the battery is degraded but phone is working 100%. Yay!
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The full story...
Root cause analysis: I now think it