Just an update - this charger is deeply unreliable in repair or test mode.
Here’s a seemingly healthy Eneloop battery which is 2 years old:
The charger gets stuck at 0% constantly, 3 of the 4 batteries here were stuck here at 0% despite giving the charger days to sort itself out.
Power cycling it causes it to recognize the battery’s actual charge, here it is after power cycling:
It then gets stuck again after a few hours.
Would recommend folks avoid this charger until they sort out its issues.