Can a Victron SmartShunt also show my starter battery voltage, and how is the Aux input wired?
One Aux input, three jobs, pick one
The SmartShunt monitors your house bank fully and one extra parameter through its Aux terminal. Victron's manual lists the three options:
| Aux option | What you get in VictronConnect | What connects to Aux |
|---|---|---|
| Second battery | The voltage of a starter or auxiliary battery | Second fused red cable to that battery's positive |
| Midpoint | Midpoint deviation of a 24V or 48V series bank | Second fused red cable to the bank midpoint |
| Temperature | Battery temperature | The BMV-702/712 temperature sensor |
It is one or the other. A trailer with a 12V lithium house bank and a lead-acid breakaway or starter battery usually picks the second-battery option, which is the question most owners are asking.
Wiring the starter battery option
- Check the negative. The starter battery's negative must be connected to the SYSTEM MINUS side of the shunt, not the BATTERY MINUS stud. Victron's procedure starts with that check, because the shunt reads the Aux voltage relative to its own system side.
- Push the ferrule pin of the second red cable with fuse into the Aux terminal on the shunt.
- Land the M10 lug of that cable on the starter battery positive.
The SmartShunt ships with two fused red cables: one is the Vbatt+ sense lead for the house bank, the other is for Aux. You do not need to buy a cable for this job.
If you choose temperature instead
The temperature sensor is sold separately, and Victron warns it is a different part from the temperature sensors packed with inverter/chargers and some battery chargers. Its black wire goes into Aux, its red wire into Vbatt+, and its lug onto the house battery positive, which means the two fused red cables are not used at all. Temperature matters most on lithium charged in a cold compartment, because the SmartShunt can pass the reading to a Cerbo GX for charge control. If you want both a starter voltage and a temperature, that is a second monitor, not a setting.
What the app shows
Once Aux is set to "starter battery" in VictronConnect, the starter voltage appears alongside the house bank's state of charge. There is no state-of-charge percentage for the starter battery, because the shunt does not sit in that battery's current path; it is a voltage readout only. For a trailer, that is enough to catch a breakaway battery that is not being charged.
SmartShunt or BMV-712 for this
Both have the same Aux input with the same three options. The BMV-712 adds a panel display and a programmable relay that can act on a low starter voltage; the SmartShunt relies on the app and, with a Cerbo GX, on VRM alarms.
What you need
Want the full walkthrough? Read the complete guide.