Actually, what a normal CC/CV charger does is to start in a current limit mode, where the cell actually determines the voltage level. As the cell gets fuller, it becomes harder for the cell to accept the same current level, so the voltage rises. When it gets to about 3.65V, the cell is almost full (85-90%...). After that, the voltage starts rising at a much quicker rate. To get the last 10-15% in, you need to hold the voltage at the cutoff, and let the cell gradually taper off the current.
With SLAs, you can do this at the pack level because the cells can chemically aborb extra current at the cutoff, so they self-balance. With Lithium-based chemistries, you can't let them overcharge, especially high-powered LiCo cells, which tend to blow up when over-charged. LiFePO4 cells won't blow up but continued overcharging will shorten the longevity of the cells.
In any case, what is needed is a proper CC/CV charging profile. If the cells were all exactly the same capacity, at exactly the same SOC and have exactly the same internal resistance and are all at exactly the same temperature, you could use a single CC/CV charger, set to have a crossover of about 3.65V x the number of cells. The reality is that the cells really need to be able to hit the crossover point at their own pace, and taper the current off at their own rate as well. One solution is to use a bunch of individual cell CC/CV chargers. I still have a setup of 16 of the Voltphreaks 2A CC/CV chargers, and they do the job. Two problems, though. First, you need to bring out all of the junctions for each cell to outside the pack. Secondly, the Voltphreaks chargers are only 2A, so it takes a long time to charge a fairly drained pack.
The cheap Chinese BMS units that come with most of the duct tape offerings leave the CC/CV control to the single bulk charger, and then afterwards tries to bleed off the higher voltage cells to the level of the lowest. The problem is that without individual CV control for each cell, the high cells will start the quick voltage rise before the low ones can get to the cutoff point. The charger just sees the total voltage so as soon as the total hits the crossover point, it holds it there which will cause the high cells to start dropping the current. Since all the current has to go through all the cells, the low cells don't ever get a full charge. Then, the balancer will then start pulling down the the level of the high cells to that of the lowest one. Sure, they might eventually get balanced, but it will be to the lowest common denominator. What you really want is for the cells to just get as full as they can, whatever that level happens to be.
With the shunts, you get the best of both worlds, individual CV control, but a simple bulk charger. The way it works is that once the cell's voltage gets to 3.65V, it is held there and the cell gradually reduces the current it takes in. The trick is that whatever the cell doesn't take in, is bypassed by a big Darligton pair power transistor. If the cell is almost full, most of the current gets bypassed. This way the next cell in series has all the current available to it that it needs, and so on, down the line. The charger just keeps pumping out the max current, and the cells use as much or as little of it as they need. Since the current never reduces, the charger's shutoff feature, it it has one, is not used. Instead, the BMS logic detects when all the shunts are in full bypass, and then cuts off the charge current completely, which then will trip the charger's low current end-of-charge detection logic. On the BMS, you will see all the orange LEDs go off, and the green one come on.
Anyway, because the shunts are really controlling the CV mode(s), a regulated supply could be used instead of a charger. What Bob was refering to is that the signal that cuts off the charge current, and turns on the green LED, could be used by some chargers, or suppies, to stop the charge process. The only charger I'm aware of with this capability is the $450 Zivan NG1.
-- Gary