I have had 3 nitecore chargers. I2 I4 and a D4. All three had bay failures in less than a year of ownership.
I now use a VC4 Xstar. I'll only own Xstar or Opus from now on. Jon had commented to me before that he has never had that problem with all the Nitecores he has sold. You are the second person that had told me they have had the same problem.
I'll never buy another Nitecore product again.
Not saying they've never had a problem but the failure rate is very small and definitely acceptable. We see a little lower failure rate than Efest, but both are good. Did you guys have the newer I2/I4? Or the 2014 or earlier one. The new one seems higher quality so far.