question

The "Charged voltage" from the SmartShunt/BMV does not control the battery charging. It is just one of the parameters used for SOC synchronization to 100%.

When using ESS, the battery charging voltages are those set in the inverter. But you should also set them (same values) in the MPPT chargers, too (for instance if the communication cable is unplugged, then the MPPT will still use correct voltage values).

You mention "Networking". Do you mean VE.Smart Networking? You should not use that for ESS. Connect the chargers with cables to the GX device.

My bad, I see that the charge voltage in the "Networked Operation menu changes with solar, so obviously it's showing the "Charging voltage" not the charge voltage as such, it was fixed at 54 when I wrote the question because there were clouds and little solar, so just showed the battery level. But the question still stands, the battery won't charge above 54 so where is it being told to stop there?

Maybe this helps

MPPTs show two voltages, Panel and what they see from the battery connection. Assuming good wiring, this is battery voltage to within a few hundredths of a volt.

Shunt shows battery voltage as measured.

Charging is three phase and four phase on the MPII.

First phase, bulk, is simply pump as much current in as the batteries will take, limited by the max current setting (under ESS/DVCC control). During this phase the battery voltage increases.

Second phase, absorption, is fixed voltage - once the configured absorption voltage is met, the charger maintains this voltage and the batteries continue to charge, but current will drop as they become more charged.

Third phase, float, is a lower voltage, and keeps the batteries fully charged.

Fourth phase, if configured, is storage. this is an even lower voltage and is to stop the batteries from degradation due to self discharge (most useful for lead acid).

Notice I haven't mentioned your Charged voltage yet. This is only used by the shunt for state of charge (SOC). When Charged voltage is reached AND current drops to the tail current setting for the specified time period the Shunt resets state of charge to 100%. From then on it calculates SOC based on current in and out of the battery. If it didn't work this way, measurement inaccuracies add up and cause drift in the SOC displayed.

The 54V you're seeing is either the actual battery voltage at the time, or the shunt parameter charged voltage. It is set in the shunt configuration.

Sorry to be long winded and cover stuff you mostly know, but I can't identify gaps in your knowledge and it's usually the minor missing point that causes confusion. ;-)