question

@fash, the immediate possibility I see is that the shunt for the BMV may be connected incorrectly, as it is this that measures all in- and out-bound current from /to your batteries and reports this data not only to the BMV display head but also to the CCGX. It is absolutely critical that the only thing connected directly to your battery bank NEG is the "battery" side of the shunt; ALL other systems NEGs including loads, chargers, "chassis" grounds, etc must be connected to the other side of the shunt, labeled "loads and chargers" (or sometimes just labeled "loads").

The shunt -and therefore your BMV, and therefore your CCGX- can only "see" current that travels through it, so any load or charger that connects directly to the battery is bypassing the shunt and can't be measured by it. That's how you get a 100% SOC reading while your batteries are dead, because the SOC is calculated by a measurement of the current in and out of the battery bank through the shunt, not the battery voltage... so if a load or a charger is bypassing the shunt, the BMV doesn't know about it and can't adjust the SOC up or down accordingly.

Another common mistake is an inaccurate Ah capacity being entered into the BMV upon initial setup, which makes the BMV think that the SOC is different than it actually is. In your case, if your (4) 200Ah AGMs are connected in series to 48v, of course your battery bank capacity is only 200Ah... it's worth checking that someone didn't accidentally enter 800Ah as your capacity, as that's a fairly common miscalculation.

One other fairly common mistake to consider is that the shunt is connected backward, that is, the batteries being connected to the "loads" side of the shunt and the loads connected to the "battery" side of the shunt, which results in the BMV thinking a load is a charge and it therefore reports an inaccurate SOC, so that's something to check as well.

From what you describe, I virtually guarantee that you either have both loads and chargers that are bypassing the shunt or you have an inaccurate Ah capacity entered into your BMV... or both. Check and correct as necessary and then report back to us if the system is still misbehaving!