Wow! Thanks Joh this is good to know, as the locking mechanism on the battery holder is quite fine. It is just one tiny arm of the small separate plastic tab you twist to unlock the holder that broke off, so I will try to source a replacement tab.
Meanwhile looks like noone else on this forum reports having had the same problem. I did come across a photo of another AA battery holder with the same problem. But I also need to acknowledge the reason this tab broke off was most likely because I tried to turn it in the wrong direction due to other thoughts going on in my mind while trying to swap to a new set of batteries in the middle of a photo shoot.
Fortunately I can still twist and open the latch of the battery holder I have with a pen, so this little piece of plastic breaking has not bought my whole system to a standstill. I also appreciate you taking the time to reply to this post about a small though critical part of a legacy piece of gear.
