What is grounding anyway
Grounding your auxiliary battery system to your vehicle provides a return path for electricity to flow back to the negative terminals of your start battery and alternator. Poor grounds can result in erratic behavior or intermittent problems with your auxiliary battery system as well as heating, arcing and even fires. This part of the circut is just as important as the positive connections and cables.
Why we don't recommend frame grounding
The frame is often shared with multiple electrical circuits, such as lights, sensors, and the engine control unit. Grounding the auxiliary battery system to the frame may introduce unwanted electrical interference, affecting the reliability or performance of sensitive electronic devices such as radios.
Corrosion and Rust
Off-road conditions expose the vehicle's frame to harsh environments, including mud, water, and various contaminants. Over time, this can lead to corrosion and rust on the frame, negatively impacting the grounding connection and overall system performance.
Vehicle frames are typically made from steel which is not an efficient conductor. The electrical connection between the frame and body to the negative start battery terminal is not always sufficient to carry the large amount of current a typical DC-DC charger will draw from the vehicle's electrical system. This results in electrical resistance, voltage drop, and in severe cases damage to the vehicle or electrical system.
Advantages of grounding to the start battery
Grounding to the start battery creates a dedicated pathway for the auxiliary battery system, isolating it from potential interference or disruptions in other vehicle systems. This isolation enhances the reliability and stability of both your auxiliary battery system and vehicle's electrical systems.
Connecting the auxiliary battery system directly to the start battery significantly reduces resistance in the grounding circuit, resulting in improved performance and efficiency.
Read your manual
Your vehicle's manual may have information on how to connect accessories to the vehicle's electrical system. If available, be sure to read and follow any manufacturer's recommendations or instructions.