MBP Early 2015 (A1502) has died! Went to use my MacBook two days after switching on with no issue. When I went to boot it was completely dead. When I went to charge it, there was no light. 

I left it on the charger for 20 mins and returned to a solid green light. I did an SMC reset which set it back to amber. The MacBook booted and worked fine for around 4 mins. The battery was registered at 32% (think it’s only around 420 cycle). It suddenly died, and returned to a solid green light. 

I left it to charge where I noticed it flick between amber and green, but then was permanently green. Still no boot so took the charger off and went to put it back on and it’s been dead since! 

Any help would be appreciated! I have the parts ordered that’s  needed to open and try restart the battery.
this sounds like a Hardware Issue definitely. I have the same A1502 model. I have never seen any Mac do this but if you can connect the MacBook Pro to its charger then startup, you should press "D" while its starting. This will allow it to check itself for issues. If you are convinced that its a software issue, you can try booting up from macOS Recovery and reinstalling macOS. Good luck!