Good post from DrewE, one size doesn't fit all. Also what is a battery monitor and at what accuracy? A volt meter, a amp meter, Ah or Wh, accumulated power, some time related information, etc.
I would be cautious about installing a shunt near the converter. There may be loads from there to the battery, if not amps will be accurate but volts will be lower due to wiring loss. My full function battery monitor has wires directly from the shunt and + - battery and hence it knows and tracks battery power. From my experience the hall-effect current sensors are not as accurate as the shunt type.
There are lots of options.
I have a $20 "battery monitor" with shunt that displays V, A, W and Wh that I use to monitor the supply for a pricey radio. It only measures current in one direction. With a manual reset it displays Wh and hence the discharge and SOC starting with a fully charged battery.
