Emile O

That is true, but the values it sends are practically static. It sends a static 53.2V as a charge voltage (and 52.5V is a better alternative), and the charge current limit (CCL) is 25A per brick, which it lowers to 12A when it gets to 99% full. If you exceed the 12A... nothing happens. The battery is pretty forgiving about everything except voltage: If you exceed 54V, it switches off.
In other words, there is almost no difference between following the instructions of the BMS... and just setting 53.2V and a 25A (per brick) limit in your inverter config. The latter will work just as well as the former in the vast majority of cases.
It is a good thing to connect whatever means of control the BMS has, but what I mean is that the BMS should not have to send CCL=0 to tell me to stop charging, unless it's an emergency. Ideally the BMS should only send CCL=0 when it's absolutely imperative, in other words, when damage will result if I don't, and then it should activate its own self-protection if the inverter/charger does not comply.
A two-signal analog BMS can send a CCL=0 (and DCL=0, discharge current limit) just as effectively without the cost of the CAN-bus electronics.
There are many BMSes that send CCL=0 when the battery is full (and it is my opinion that they should not, they should not intervene in this way). This includes BYD B-Box pro as well as the new 24V Pylontech batteries. If you do that, you get a sawtooth voltage and SOC chart, because the charger stops charging at 100%... then starts again at 99%, causing these little micro-cycles at the top. Voltage control is better. Once you reach the target voltage, current automatically stops flowing because there is no potential difference.
So don't get me wrong, I do like the CAN-bus bmses and the communications. It is a good idea. You get SOC tracking from the horses mouth, you get information about cell temperatures, some BMSes can even tell you the bitmask of the balancer (which cells it's bleeding off), and of course it can communicate alarm conditions. But it's not like you cannot live without it.
On my system I have Victron LiFePO4 batteries with a VE.Bus BMS. This is essentially a two-signal BMS. Not a day's trouble...

I'm with you as far as inverters that are either old and cannot be upgraded, or simply do not support BMS connectivity with a certain battery.
I was not aware of the current measuring capabilities of some inverters that you mentioned above, so that's some more useful information, thanks for that. 
I also don't dispute that the systems will work in User mode with manual config, and you can do that, but I'm still very skeptical about it working optimally and batteries being managed the best they could be if the BMS is not involved.
My real issue is with new inverters being sold with Li batteries that have a BMS, and then not working properly with those batteries, and then the supplier or installers tells the customer its not necessary and proceeds to work around the BMS by using a User profile.
That is not acceptable to me. If the inverter is not capable of BMS comms and cannot be upgraded with new firmware to support BMS comms, then it shouldn't be sold with those batteries.
That's exactly what happened to me recently and if it wasn't for the fact that I'm very technical, very persistent, not afraid of deploying firmware to anything, and refused to accept the 2nd prize solution, I would also now probably be running this inverter in User mode, and that would be a great shame because the whole system works far better and is far more accurate with the BMS active and in control.
Obviously if people are buying inverters and Li batteries privately and not through an installer, they also have a responsibility to do their homework properly and make sure they are buying an inverter that IS compatible with the BMS of the batteries they choose. But even then, the suppliers they buy from need to be responsible and tell customers when an inverter is not going to work with a certain BMS and warn them that combination they've chosen is not going to run optimally, using the BMS.
 
 
 
 

I've new to this game and I've been doing a lot of research lately and I'm concerned about one specific topic that keeps on coming up and seems to be causing a lot of confusion:
Why the BMS (Battery Management System) that is built into your expensive new Lithium battery should ALWAYS be connected to your inverter via a comms cable, properly, unless its physically not possible.
I'm seeing a lot of information about how BMS's are being bypassed completely and effectively ignored and inverters are being put into non Lithium specific modes (User mode) and configured manually so that they monitor the Lithium batteries using voltage monitoring only, as if they are the old Lead Acid or Gel type batteries.
And there seems to be a lot of acceptance that it's perfectly ok to do that and that the BMS really makes no real difference and it doesn't matter if your inverter is communicating with the BMS over a comms cable.
I have a real problem with that philosophy for a few reasons, and if you understand what actually happens when you connect your inverter to the BMS properly and proper comms is established, it becomes very clear why that is always a far better option.
Things to know and understand:
1. The reason you paid so much money for your new Lithium battery with a built in BMS is because that battery is not like the old Lead Acid or Gel batteries which are literally just a group of cells joined together with a positive and negative terminal.
The BMS built into Lithium batteries is a computer and is monitoring the internal state of your battery down to cell level micro voltages. It is aware of everything going on inside that battery and it knows when the battery needs to be charged, how much current it needs to draw, exactly what the current SOC (state of charge) is (as an extremely accurate % value).
2. When inverters are only connected to a Lithium battery via the voltage leads, and ignore the BMS, they can only use the voltage level they are monitoring across those voltage leads to make any decisions related to discharging the battery or trying to show you the current SOC of your battery (which they have to attempt to calculate based on voltage floor and ceiling values that you've manually configured and the voltage they are currently seeing across the battery terminals).
That does work, but it's not nearly as accurate as the BMS is.
The problem is that:
       a. Most inverters, particularly cheaper ones (under 20K ZAR as a generalisation) don't seem to be able to detect very fine grained changes in the voltage across the battery leads. And consequently they aren't able to give you a SOC value that is dead on accurate to what is actually going on with your battery. Depending on how coarse grained the voltage monitoring of your specific inverter is, the changes in charge level that you will see displayed will vary all over the place and it will not change by 1% at a time, it will jump values (random example: It might drop from 95% straight down to 90%).
       b. Lithium batteries have a narrower voltage range between fully discharged and fully charged, than the other types of batteries, and that makes the situation even worse for inverters that can't pickup small voltage changes because smaller changes in voltage now mean bigger changes in SOC.
3. If you get your inverter to talk to the BMS correctly, as intended by the battery manufacturer, the following happens:
     a. You have what we refer to in the software industry as an "inversion of control".  This is very important to understand. When the BMS establishes proper comms with your inverter the BMS TAKES OVER responsibility for what happens to the battery. In that scenario the BMS is now in control and NOT the inverter. That is why an inverter that is properly connected to an Li BMS, and is put into a proper Li mode, LOCKS multiple settings related to voltage floor and ceiling, charging current limits, and some other things. The reason is because the inverter is no longer responsible for deciding those values, and neither is the user (which is why you can't set them), the BMS is. 
The BMS now constantly reports it's SOC and other relevant information to the inverter AND it will tell the inverter when it needs to be charged etc. The inverter just does what it's told, how it's told, when it's told.
The inverter will also now display real time, extremely accurate SOC values and real time charge current values etc., because those values are constantly being sent to it by the BMS.
    b. If you have multiple batteries stacked, then one of those batteries is the master and the BMS will act on behalf of all of the batteries in that stack and make sure that charge is evenly distributed to all batteries and that things are always in balance across the stack.
 
The bottom line is that if you have Li batteries with a BMS, you should always want your inverter connected to that BMS properly, and using the old voltage monitoring approach is NOT the same thing.
I fully understand that if you have an older inverter you may be in a position where there is no new firmware available and it doesn't have an Li profile and can't communicate with a BMS, in which case you have no choice but to rely on voltage monitoring, and you still get multiple benefits from using Li batteries.
My problem is with brand new inverters being setup to willfully bypass the BMS on expensive new Li batteries and being configure to run in USE (User mode) and use voltage monitoring and that being considered perfectly acceptable and ok.
I've personally just spent 80K ZAR on a new battery backup system with a 5Kva Growatt inverter and 2 x Pylontech US3000 batteries and it took me a week of communicating with Growatt in China and doing my own research to figure out why my new inverter would not communicate with the BMS correctly (during which time I had USE mode and voltage monitoring active as temporary workaround). But I refused to accept that the inverter would not connect to the BMS properly and eventually I resolved the issue, upgraded the firmware, and got it right.
And now my system is far more accurate and I know that those very expensive Li batteries I bought are being managed properly and not abused, and I know that the information I'm seeing in the monitoring app and on the inverter display is dead on real time accurate.
If your new inverter is not connecting to your BMS properly then in my opinion that's a problem and needs to be addressed. New firmware must be provided if necessary to upgrade the inverter to be properly compatible with your batteries, and proper documentation must provided explaining exactly what type of cable needs to be used for BMS comms in your specific case, what dip switches need to be set on the battery (if applicable) and what mode the inverter must be put into to trigger proper BMS comms and run in a proper Li profile.
There is a reason we are paying 20K per battery for Li batteries with fancy BMS's built in.
Please use them.