I am running a 400Ah 48V lithium pack (self-built) and monitoring it using the Multiplus II 5000 internal battery monitor. The system is a grid parallel ESS setup.
It has Daly 250amp BMS (not interfaced with Victon at this stage).
Is there some margin to using a smart-shunt to measure the battery capacity and SoC?
Is it more accurate? If so, why?
Yes there is.
The multiplus does not have a shunt in it for measuring the current down the battery. So that is the main difference here. And shunt measurement is always more accurate if set up correctly.
The VE Bus SOC has been imporoved a bit in the newer firmware where it can use current sensing from the mptts and what was used by loads to work out a bit better what was sent and used from battery.
I do have one system without a shunt and have noticed that the internal monitor is fairly accurate if your system gets to a full charge each day and stays up and you have grid available.
On a mostly solar off grid type set up, it is not as reliable.
If you are big on a more granular monitoring of your system though, get a shunt.
