I too have a similar problem to this, when my battery meter reaches around 46-45% the phone shuts down without warning.
When this happens the phone refuses to reboot or charge the battery
if I take out the battery and place it in another 9700 it starts to charge..Once it has received as little as 1% charge in that phone
I put it back into the other one and it continues to charge.
I bought a new battery, the problem remained. I upgraded from OS. 5 to 22.214.171.1248 and the battery last about 5% longer but that’s it
At maximum charge the battery reads 4120MV...at 15% it reads 3618mv. If the 100% reading is correct then at 15% the MV reading should be 618MV.
At a lost as to why this is occurring, would welcome any input on how to solve this problem.