New MBP Battery Can't Handle Stress, Unexpected Power Loss

I recently ordered a replacement battery from iFixit to replace the machine's original OEM battery, which was degraded significantly. It was then installed by a certified Apple technician. It worked more or less perfectly for a while, even with greater amp-hours than promised, but when running a game or other software that revved up the GPU or consumed a lot of power otherwise, the machine would suddenly enter hibernation, if connected to AC. If going on battery, the machine would simply suddenly shut off, even with ~80% charge left.

I returned the first battery, believing it was defective, and ordered another. This second battery is displaying the exact same behavior, and I'm wondering if I've ordered the wrong part, the battery simply isn't any good, or if there's a deeper problem with my machine. The OEM battery has been recycled so I can't use it to test.

The part I ordered: [product|IF163-054]

The output of running `pmset -g pslog` in Terminal:

• InternalBattery-0 (id=4718691) 100%; charged; 0:00 remaining

Detailed failures: "Externally Indicated Failure", "Safety Over-Voltage", "Cell Imbalance", "Discharge FET" present: true

• In addition, when I run in Terminal, `pmset -g log` there are lines that look like this:

2018-01-10 01:52:18 -0600 Sleep

Entering Sleep state due to 'Low Power Sleep': Using AC (Charge:100%) 89 secs.

I don't think the machine should be getting a low power signal while on AC with a full battery. Any help would be appreciated.