New battery charging wattage fluctuates and stuck at 99% - Lenovo Y50-70

I recently replaced the battery in my Lenovo Y50-70 with a new one from iFixit (L13N4P01/L13M4P02). Since installing it, I am seeing the charging wattage fluctuate constantly between 0.0 W and 38 W every couple of seconds.

The battery also seems stuck at 99% and never reaches 100%, even after an overnight charge. I have already tried the calibration process (charging to 100%, draining completely, and charging back up), but it didn't solve the issue.

Critically, when I reinstall my old battery, the charging is stable and does not fluctuate. I have also verified that my AC adapter (20V) and DC-in jack are working perfectly.

Has anyone else experienced this specific fluctuation with a new battery on this model? Is there a BIOS setting or a specific driver reset that might help, or does this sound like a defective battery pack?