Hi Chris, AGM’s definitely have their place due to low maintenance and no off-gassing, but one downside is that they (the cells) cannot be equalized to reverse the effects of sulfating overtime, which may also impact longevity…And since they are still considered ‘wet-cells’ voltage will normally sag as the SOC (state of charge) drops off…
As such, this can ‘sometimes’ (particularly when aged and sulfated…) lead to a mild discrepancy between what a shunt based type SOC meter reads versus actual measured voltage as it relates to SOC…The Victron (or equivalent LinkLite or Trimetric) uses a shunt device (installed in the battery negative cable) which once programmed kinda works like a amp counter to arrive at SOC…
Having said that, regardless of which battery type, I believe that a shunt based SOC meter is an invaluable ‘MUST HAVE’ tool to help understand what the actual condition of the battery is…The ‘sometimes’ discrepancy I previously mentioned tends to be virtually non-existent with LiFePo4 lithium due to their near stable voltage characteristics…
