Thanks for that!
The largest battery I have is a Sofirn 21700 5000mAh flat-top (came with my SC28); I don’t have calipers but from the data I can get from Sofirn and from @HKJ’s review it should measure between 70.6 and 71.1mm (@HKJ measured 71.0, Sofirn says 70.9+/-0.3) and it’s a VERY tight fit with barely a small fraction of a millimeter to spare:
(picture of the MC3000 bay’s rear terminal with this battery on it).
And let me tell you, it was a real PITA getting this battery in there, took me a minute of pulling the rear terminal as far open as as it would go with a finger from my left hand, and then using my right hand to try and wiggle the battery in there.
SkyRC should have made the bays longer, even 5mm would have been a big help, but a full centimeter would have been even better. I hope they revisit that in a future edition of this otherwise awesome charger.