MacBook Pro mid-2012 turning on only without battery connected

My MacBook Pro mid-2012 is barely 5 months old and it just won't turn on one day. MagSafe Adapter doesn't show green or orange LED while charging. LED display did not show any lights either.

Following online instructions, when I opened it up and removed the battery connector and plugged the MagSafe adapter. Adapter started working well and LED lights too.

I heard it boot up but nothing on screen. Puzzled, I hooked it up with a monitor and I could see my login screen but my keyboard and trackpad were not working as well so I could not do anything. I tried doing SMC reset from there that did not work either.

As soon as I put the battery connector back, it stays on only until I remove the MagSafe adapter even if battery is fully charged. Has anyone encountered a similar issue and solved it?

It’s almost certain the battery is the failure here, but if you had access to a replacement part or didn’t mind spending money on a new MagSafe connector, you could try replacing that first.

The battery is almost certainly the cause dragging the voltage and/or current too low for the system to start. The chance the sensors that check the voltage and current are correct and it’s actually a low current and/or low voltage situation and swapping the battery with a good one would remedy that fault.