Thanks Wayne,
I see you reside where some of my former co-workers from BNP have retired to!
I am ordering a Frey M600 package. They have agreed to ship it with an empty battery case that I can populate myself. I have about 120 LG M50 21700 cells enroute, half of which are to build a battery for a portable repeater I'm working on. I will have enough to complete the battery for the bike as well, and I can build it out at 13S or 14S. Obviously, the 14S (52V) option would be preferable. As I need to tell our battery supplier which BMS's to include with the order, it would be best for me to decide now which build I plan to do. I'm tempted to build the 14S, and then perhaps charge it with a 48V charger, which I already have on hand. Then in order to balance the cells from time to time, I could give it a full charge from a 52V charger, and, if I still have concerns about the higher voltage on the full charge, perhaps run it down before mounting on the M600, similar to what I think you did.
Of course perhaps I should just build the pack to 48V and be done with it. That would also have the advantage to me of not having to buy a charger because I already have a 48V charger anyway. At the moment I am riding a Giant Full-e, and I think that the M600 would probably satisfy my wishes even at 48V.