Midnite Solar Shunt 500A 50mV DC current, brass with insulated base
A shunt is necessary in order to measure amps and amp-hours with a battery monitor. A shunt is an accurate, very low resistance resistor which is placed "in line" with the wire carrying the current to be measured. It is usually placed in the negative wire from the battery bank, such that all the current going into the battery (charging) or out (discharging) must pass through it.
The 100A model is scaled to read 1 mV per amp, while the 500A model reads 0.1 mV per amp. Brass with insulated base.