Drake Jest, This sounds like the device can’t get enough power from the battery in order to perform as expected.
I don’t have experience with this particular device, but most devices like this you can use both with power connected “on top” of battery. If you connect external power, and then run same tests again, does it still do this?
Many low quality aftermarket batteries don’t hold enough power to perform like original. It’s always best to purchase batteries (as most things) from reputable vendors. They do their own QC and they have a great return policy, should there be issues.
If you connect external power, and the problem disappears, you know 100% that the battery is at fault.