New battery installed. Charges up to 100%, runs down to 50% then suddenly instantly drops to 7% and stays there for about 2 hours. Battery seems to continue to work but metering is wrong. Tried all the usual tricks (Battery conditioning, SMC, PRAM, NVRAM, Reboot, Reinstall MacOS...etc) with no solution in sight. Any ideas? Just a crappy battery? Apple asked for $700USD for a replacement so I bought an aftermarket one for 1/10th of the asking price.
It seems you have already tried all the things that can be recommended in your case. I would assume your battery is faulty.
For anyone else with this model reading the thread: if you do have a Mid 2015 MacBook Pro your battery might be eligible for free replacement unter a quality program: https://support.apple.com/15-inch-macbook-pro-battery-recall
You could check for the QP as well Vaultnaemsae, but chances are Apple is going to decline coverage as you already performed unauthorized service on the machine (and your Apple battery is no longer a threat as you took it out, which would be the whole point of Apple replacing it free of charge.)