Rocker-switch-style dual digital voltmeters, specifically designed to monitor dual battery setups in vehicles like trucks, 4x4s, RVs, and boats.Key FeaturesDual Monitoring: They simultaneously track real-time voltage for both your primary engine battery (MAIN) and an auxiliary backup battery (AUX).Standard Fitment: Designed to snap directly into a standard Carling / ARB rocker switch panel cutout.