I have MBR Mid 2012. I followed all the instructions and was able to successfully remove the battery and replace with iFixIt’s OEM battery, took me about 2 hours. A couple of issues I ran into that I think might help few people here.

1. Fan Cables - at the other end of the fan cable, there is a small latch you have to lift from the board for safe release. Same goes for most of the flat styled cables on this entire motherboard. Also make sure to re-seat it with precision. My computer once booted reported at Hardware Check that one of my fan was at faulty and indeed noticed my right side of fan wasn’t running. I had to reinstall the cable a few times to just get it right so it would start spinning.

2. Battery Calibration - If your Macbook is shutting down below 20% or so and SMC/NVRAM reset didn’t do the trick, try this old method designed for older generation of Macbooks. Unplug the Battery cable, hold down the power button for 10 seconds, re-seat the cable and boot. Charge too 100% and let it drain.