Review on ⚡️ MICTUNING MIC-DV-077 LED Digital Panel Double Voltmeter with Rocker Switch Style, Blue Voltage Monitor for Car Pickup RV Truck Dual Battery Pack by Sean Sheppard

I used this when installing a dual battery system. Unfortunately it doesn't read the voltage from the second battery where it is connected to the insulating solanoid with a 4 AWG wire. I suspect it has something to do with the 4 AWG wire resistance since I can correctly measure the voltage with a voltmeter. I suspect I need to run a wire to the trunk where the second battery is installed. So far, the readings have been accurate for the first battery. I really wish it had an off/on switch as it's basically "always on" and while it's not a big deal the voltage is so low after 48 hours of car sitting that the car won't start, without activating the secondary battery.