MacBook Pro shuts down during boot. Strange Issues

I am an experienced certified ACMT/ACPT tech since OS 7.5 but in a kind of semi retirement and looking now at fixing macs as a hobby. The following issues are with a MacBook pro:

1. I have done the SMC and PRAM reset (Pointless for PRAM since chime does not come, For SMC - Charging light color does not change if at all it is on)
2. Diagnostics gives a code PPT001 (battery not detected) and PFM001 (SMC Issue)
3. Charging light does not come on. If I connect the charger to a good computer & then connect to the problem MacBook Pro - the light glows. But if the light is green on the good computer then its green on the problem MacBook Pro. If its amber on the good computer then its amber on the problem MacBook Pro.
4. Computer does not come on when amber light is on. It comes on (as indicated in #5) only after 2 hours of “charging”.
5. Computer does not power on just like that after a cold start. I need to hold down the power button for 10 secs without the charger and then holding the power button, connect the charger (after connecting to an amber good computer) for another 10 secs and release and disconnect the charger.Then I press the power button. There is no chime but loud fan noise (only fan towards the charging port works, other one does not). There is a considerable time between power on and the appearance of the flashing folder or boot choices (on pressing Option)
6. The inbuilt SSD does not get detected (I get a flashing question mark folder). Inbuilt SSD has Mojave on it. However if option is pressed, booting commences on external drives. Detects bootable bootable drives having El Capitan, Sierra and High Sierra. Does not detect drives having Catalina.
7. While booting, progress bar goes to halfway and abruptly shuts down. Repeated tries are similarly unsuccessful.
8. In verbose mode, it stops at “waiting for DSMOS”
9. Using Command line, I shifted the AMD Kexts out of the Extensions folder, hoping it to force using the inbuilt Intel Graphics assuming the AMD graphics has gone bad. Same problem.
10. I have reset the NVRAM through command line, same problem.
11. I have downloaded the Firmware Update 1.0 from Apple and tried installing from command line, it says the computer does not need this update.
12. I am unable to get the firmware version using “/usr/libexec/firmwarecheckers/eficheck/eficheck --integrity-check” I get a message something bad command or directory.
13. All command line functions work ok. It even fires up Emacs.
14. Its not that the machine shuts down due to temperature tripping. I have worked for about 2-3 hours in the terminal mode. In fact the fan noise substantially comes down (compared to initial start up) but not silent.
15. I tried Recovery Mode, again it crashes when the progress bar is halfway.
16. Safe Mode (pressing Shift during boot) does not work. Computer shuts down during boot. Shift key works during single user mode.
17. Essentially the computer does not get into GUI mode at all.
18. The display is dim, the chime doesnt come. Ocassionally if i press the power button I get the continous beep sound with uniform intervals.
19. During activity, if the charger to pulled out, the computer goes dead.
20. In Recovery / Diagnostic mode it ask to connect to wifi and it connects normally.
21. Pressing T during boot shows the Target Disk Mode on screen.
22. Caps light lights up during verbose mode
23. To sum up, we have (1) no start up chime but beeps sometimes for error (2) no internal drive detection (3) One fan spinning too fast, One fan Dead (4) Dim Screen (5) Strange charging behavior (6) a possible dead battery
24. My feeling is that the SMC seems to be bad, needs to be flashed and re programmed.

Would be grateful if someone helps me out on this. I understand that if the computer seems beyond hope but this is the best Mac Apple has rolled out in a decade!