Chosen Solution
So my battery was on it’s way out but I procrastinated. Well go to start my laptop and nothing. Pull the battery and try to boot just off AC power off the 85w charger that came with it. Nothing. The light on the magsafe is pale green. No amber. Sometimes goes bright green but nothing. Reset SMC, PRAM and NVRAM (doesn’t boot so idk if it does anything). I know some MBP’s can run off just being plugged in. Is mine not one of them?
Yes, yours as well would run off mains without battery plugged in. Check connectors are well in the sockets and see if there’s any obvious sign of damage on the board, magnification and good light source would help. Quite weird the green led dims at times and is bright green other times. Would be good to make sure you’re using a good working charger by borrowing another one form a friend or check yours works properly on another Mac. When led is bright green your Mac should start on its own without power button.
Sounds like you have some corrosion damage and the charging logic on the main logic board may need repairs.
I would recommend unplugging the charger and battery then pressing and holding the power button for 10 seconds then pressing and holding the power button while plugging in the charger and then quickly release and press the power button. If this works then it might be something with the charger.
