The question is – is your drive t2 encrypted? I guess not because it is from 2015. If not them you can try Paragon HFS+ https://www.paragon-software.com/home/hfs-windows/

Do you have the FileVault password?

You can run a Linux VM on Windows using something like VirtualBox or VMware, then pass your Apple SSD enclosure through to the VM, but while Linux tools such as apfs-fuse or apfsprogs can mount unencrypted APFS/HFS+ volumes, support for FileVault encrypted drives is very limited and often unreliable, even if you supply the correct password, so although you can experiment with a Linux VM it is generally much easier and more reliable to connect the drive to a real Mac, unlock it with your FileVault password, and then copy the files to an exFAT-formatted drive that both macOS and Windows can read.

Can you connect the drive in the external case to your MacBook Pro? Assuming you disconnected the battery, your could try with the power adapter connect to the Mac

and boot from the external disk. You would have to select the external disk as boot device (cmd r when you see apple

boot logo). 

I tried Paragon HFS+. It does not see the drive at all.

I put the drive back in the system, after removing the bad battery, and went through the troubleshooting sequence.

I tried ‘Cmd R’ and logged into my wireless. It gives you a meter, which completes, then it brings me back to square 1 - Apple logo.

I tried ‘D’ while it starts up and was successful in accessing the diagnostics. It ran and discovered my missing battery. That was it - No other signs of hardware issues.

I check my power adapter (no I don't have another one), cleared the SMS and NVRAM. Still NO success.

Anything else I can try before I cave an run to the Apple Store?

The last thing yo try, but not cheap..

Stick another drive in the laptop and do an online recovery to get a running OS.

Attach the old drive and see if you can recover the files…

It kind of sounds like the failing battery corrupted something in the boot up files.

I just purchased a replacement drive. I put a rush on it. Hopefully I will get it tomorrow. 

An even more expensive idea is a recovery service… Or like you did suggest the Apple “Genius Bar”…

or try GetDataBack, it will show what it can recover, you only pay for storing the data:

GetDataBack — Data Recovery Software For Crashed Hard Drives

Getdataback won't help with apple encryption either…

Just an update

Never a dull moment!

I purchased/overnighted  a drive that claims to be for a MacBook Pro Model A1398 Retina. Well it was the correct connector but actually didn't fit into the compartment space of the laptop - unbelievable!

You got to love APPLE!

I found an excellent guide to Apple's proprietary drives:

https://beetstech.com/blog/apple-proprietary-ssd-ultimate-guide-to-specs-and-upgrades?srsltid=AfmBOoqtffWiU4uCTOHyf7I7ste4TqMFQzqgg_SvdMSj4VuOSUjSnoDv

Yes I had to get more descriptive in my search for this elusive APPLE/Samsung hard drive. So, now I'm taking my chance on a used eBay drive.  It appears I like the abuse…LOL

Just in case anybody's wondering - the details of the HD:

MZ-JPV512S/0A4 

512GB SSUBX 655-1960B

M.2 2280 Express 3.0 x4

So, I received the 2nd replacement drive, popped it in - NO SUCCESS! Obviously there is something wrong with the mother board. Every once in a while I get red lines through my screen as if there were a problem with the display - then it clears up. I have tried every thing. 

So, I went to the Apple Genius Bar. Guess What ? Same thing, unable to boot. I learned a new Trick hold ‘T’ after power to get into Target Disk Mode (This is basically a peer to peer connection via a thunderbolt line). They tried to gain access to the existing drive via their systems tablet using  'Target Disk Mode'- NO Success. It didn't even see the drive. 

Apple states they are not a data recovery company. So they basically suggested I go to one of their approved service partners.

I wasn't convinced so I bought a new Mac Book Air and requested they try the Target Disk Mode one more time to my new system. 3 hours later I was walking out of Apple with my DATA COMPLETELY RESTORED.   The new system saw the drive via a thunderbolt connection to the old MacBook Pro.