I am confused because the picture shows a Lynx BMS which would give you the battery SOC or have you included that as a generic picture.
You can use a Smartshunt, but you must connect the chassis ground to the load/ system negative side of the shunt rather than directly to the battery.
See the write up in https://community.victronenergy.com/t/shunt-battery-monitor-not-reading-the-correct-soc-amps-missing-solar-decreasing-daily-or-other-misreading-problems/87