Valeur voltage batterie démarrage indiquée par le smartshunt érronée

Had a similar head-scratcher with my SmartShunt a while back — the starter battery voltage was reading completely off compared to what my multimeter was showing at the terminals.

Turned out the issue was with how the SmartShunt's aux/starter input was wired. The sense wire had a poor connection at the battery positive, so it was picking up a slightly different reference point. Easy fix once I actually traced the wire properly rather than assuming it was right.

A few things worth checking if anyone else hits this:

• Sense wire routing — is it going directly to the battery terminal or tapping off somewhere else in the circuit?
• Grounds — shared ground between the SmartShunt and starter battery needs to be solid. Even a bit of corrosion causes odd readings on the aux input.
• VictronConnect settings — double-check the aux input is actually set to starter battery voltage and not temperature or something else. Easy to miss during initial setup.

On my boat setup I also noticed the reading would drift slightly when the engine was running — alternator noise on the line. A small capacitor sorted it but that's probably edge-case territory.

Worth grabbing the Victron wiring guide for the SmartShunt specifically — the aux input is a bit fussier than people expect.

Anyone else had dodgy starter voltage readings from theirs? Curious whether this is a common one with motorhome installs in particular, since the wiring runs tend to be longer than on a boat.

@BatteryRay worth checking the voltage sense wiring on the aux input — if you've got any resistance in that circuit (corroded crimp, undersized wire, long run back to the battery), you'll get a false reading because the SmartShunt is measuring at the sense point, not the actual terminal.

On my Transit build I had a 0.3V discrepancy that turned out to be a dodgy ring terminal at the battery end. Cleaned it up, used proper adhesive-lined heat shrink, and it read spot-on against my Fluke afterwards.

Also worth confirming you've set the aux input type correctly in VictronConnect — if it's set to midpoint rather than starter battery voltage, the maths goes sideways completely.

@BatteryRay @BoxerDream — had exactly this on my boat last winter. The SmartShunt's auxiliary voltage sense input draws almost no current, so even a slightly corroded spade connector in that circuit creates a meaningful voltage drop across what should be negligible resistance.

On my setup I was seeing nearly 0.4V error on the starter bank reading — multimeter at the terminals said 12.6V, SmartShunt was reporting 12.2V. Traced it to a single corroded female spade on the sense wire rather than the main current path.

Worth noting: the aux input is not the same as your main battery connection — it's a separate thin sense wire, often overlooked during install. Clean every connector in that loop with contact cleaner, crimp fresh terminals if needed. Mine's been solid since.

@BatteryRay had this exact thing with my garden office setup. After ruling out wiring resistance (as @BoxerDream mentioned), mine turned out to be a ground offset issue — the SmartShunt's negative reference wasn't truly at the same potential as the starter battery's negative terminal.

Quick test worth doing: measure voltage directly at the SmartShunt aux terminals with your multimeter, not at the battery posts. If those readings match, your wiring's the culprit. If they still differ from the Victron app, you're likely looking at a firmware or calibration issue.

Victron Connect has a voltage offset calibration option buried in the settings — easy to miss. Sorted mine completely.

@BatteryRay the SmartShunt's aux input has a ~10kΩ input impedance — so even a dodgy crimp or a bit of corrosion adding 50Ω will skew the reading noticeably via the voltage divider effect. What nobody's mentioned yet: if you're running the sense wire anywhere near an inverter or alternator cable without proper separation, you'll also get induced noise that the Victron app averages out badly. Run a dedicated twisted pair directly from battery terminal to SmartShunt aux input, keep it away from high-current cables, and use proper ferrules on the terminals rather than bare wire jammed in. Took me an embarrassingly long time to sort this on my static van before I stopped being cheap about the wiring.