Re: Did Jack say he needs a BMS?
He's said it a number of times, because he keeps destroying batteries through neglect. I think he just needs a better attention span/common sense. If the one cell was always acting weaker than the others, just monitor it.
I think having part of your pack (or a single cell) weaker than the rest is actually a benefit. You monitor the weak link and charge before it's an issue, no need to monitor the rest.
Also, keep in mind there 2 kinds of BMS, Monitoring and Management, sometimes called passive and active. I think Jack is interested in a passive system that can turn stuff off to prevent damage, rather than the active type that can overheat while shunting and cause damage.