THE TYPICAL GENERIC BMS SPECIFICATIONS CHART BELOW, FROM
The way they work is fundamentally flawed at least during charging. The CHARGER should be balancing the cells and controlling power proportionally in controlled fashion - not a BMS trying to control it afterwards!
MY OWN COMMENTS ADDED IN RED
Not shown here directly is that the balance current is TINY at just 100mA That's simply not adequate.
And that this allows the cells to go way over voltage time and time again as the state of charge reaches the end. This can go on for days if the pack is out of balance. Every time, the high cells get pushed to an over voltage life shortening state, and are then released again. On/Off repeat...
And it WILL BE out of balance too, because these damned BMS things keep on trying to balance the cells during the whole usage cycle. The problem with this, is that while all cells may have the same voltage (3.60 volts) when fully charged, at the half way point when every cell has had the same Ah removed during use, this is no longer the case. The voltage drop in different cells not linear and different cells vary markedly. This is correct! On recharge they will all end up full at the same time. But the stupid BMS continually tries to "balance" all day long and actually UNBALANCES the pack for many hours at a time. This then means it need RE BALANCING again on subsequent recharge. So hours of On/Off/On/Off Overcharge the full cells then cut off again and again. Get ready to throw away your valuable battery.
In a correctly implemented system you do NOT NEED OR WANT a BMS setup. You need a BETTER more accurate charge system, and a means of knowing when to stop discharging them with an intelligent system. and maximum current limit should be programmed into the controller. Not the BMS!
And a set of cells, (the battery) should be selected so that its C rate is adequate with plenty of spare headroom, for the maximum Amp requirement of the motor/controller. In this way the BMS is no longer required.
As I do here
The typical BMS is really just intended as a means to sell
Lithium batteries to dummies as a kind of one size fits all method of "using" a
lithium battery. But its a dumb badly engineered solution!
LITHIUM POWERCHAIR & SCOOTER BATTERIES