MBP Discharging

My cat thought drinking my water was a good idea one evening & effectively knocked my glass over which spilt water all over the keyboard of my 2012 MBP with Retina display (A1398)

Obviously, I reacted sufficiently... Unplugged, powered off & tipped it upside down. It was 04:30 so I wasn't planning on popping the bottom off & drying the boards off properly.

I woke in the morning & in a daze went to power it on forgetting about the mishap during the night... Oh dear

So I instantly turned it back off & took it apart, obvious signs of corrosion in 2 areas so I got out the isopropyl & got brushing away, let it dry & then fired her up.

I got X Battery, high fans & slow processing so I reset the SMC & PRAM which resolved that issue...

I powered back up to my usually quiet, incredibly speedy mbp so was very pleased. All seemed well until I noticed the battery percentage was dropping even though it's plugged in, magsafe is amber so seems to be charging but it isn't, it's discharging. When clicking on the battery icon I get "Battery is not charging" & it recognises it's plugged into the power adapter.

I've replaced the power adapter, the battery & the DC-in connector to no avail. Coconut battery says all is fine but not charging, although I have noticed it cannot read the serial of my logic board, manufacture date & age. Which, leads me to believe the logic board has had it.

But here's the weird part... If I shut down (I noted how much battery was left first & was at 12%), disconnect the battery, reboot the power by holding the power button down, leaving the adapter connected & then pushing the battery connector back in the mbp turns on back into high speed fan lag mode, it doesn't recognise the battery & won't even display the battery icon even if I ask it to, Coconut battery doesn't acknowledge it's existence & the power adapter doesn't even light up. BUT! Once I shutdown & rebooted back into the normal mode using the SMC & PRAM resets, the battery had been charged up to 85% whilst I was using it in the annoying, high fan, slow speed mode.

I can't understand why it won't let me use my mbp in the normal mode & allow it to charge but in this dramatic, high powered state it seems to prevail...

Any suggestions would be marvellous...