I'm going to run on a bit so be prepared.
I'll throw this out again on the pro / con BMS debate and let you all decide if it is a BMS and if it's worth looking at during planning your system
Right now using off the shelf stuff we (Myself, RWaudio and a few others) are actually building this.
We are going at it with a top balancing, limited voltage charge protocal and LVC or LVW.
What we plan is using, one, reletivly inexpensive, isolated DC to DC Converter
attached to each battery (large format prismatics) or battery group (small formats other then prismatics) to charge it.
The DC to DC is set to be able to only charge to a specific set voltage. The DC to DC then CAN NOT/WILL NOT
over charge the cell. Since many of the DC to DC units can have a trim pot each unit can be adjusted to bring your cells in to perfect top balance.
So for top end charging we set the voltage of the DC to DC to a safe 90% for the cells. Now the DC to DC units I am using (thanks RWaudio) can pass 25 amps at 3.65 volts and will accept any voltage between 35 and 76 volts. They can be turned on and off individually and have over and undervolt and over temp protections and a lot of others I don't understand.
Chargeing power can be handled by any of a number of inexpensive units with whatever voltages within the range of the DC to DC units because of the DC to DC units built in protection protection.
Then for LVC or LVM we use a simple voltage device like the Cell Log8M to monitor each cell (large format prismatic) or battery group (small formats other then prismatics). The Cell Logs have a warning system that can be set up to monitor each cell and trigger an alarm that could be used as an audible warning or to trigger an event such as power cut back, main contactor disconnect or whatever.
So for bottom end we set the Cell Logs for some safe limit voltage say 80-90% DOD. What happens here depends on your set up It could shut you down until you fix/charge or with the proper controller back off power each time a cell log hits low voltage.
This should keep you in the fat/flat area of the charge/discharge curve and do wonders for your pack life.
As long as you plan your pack size for the middle 80-90% of your pack this shold work pretty well.
Let's face it, when you consider the above it's not unlike filling a gas tank. You should never fill a tank all the way (100%), If you fill the expansion space you're eventually going to get a boom when things heat up. Most people never use their reserve fuel, if the do they'er in trouble eventually.
Remember this is all off the shelf stuff so it's going to be a bit crude. and have some holes in it that require personal monitoring. I'll depend on you smart guys to find a way to put this all on a board, with programming to do everything including washing the dishes.
When you get down to it, I'll have a 50 cell (50, 3 cell buddy packs in my case) protective charging system with high and low cell monitoring and LVC or LVM.
You will also have very high charge rate, it could be a 48 volt dump pack with a tickle charger at home and you could carry a good variable input voltage 48 volt 20 amp charger or power supply with the car. You don't need fancy/fussy $1500.00 battery chargers. and +$1000.00 BMS.
Again using off the shelf components, I've got everything so far for $1000.00 +-10%. Want to bet what some smart EE could come up with?
Sorry, I do run on.