If you're serious about off-grid power, a battery monitor is non-negotiable. Without one, you're guessing at your state of charge — and guessing wrong leads to over-discharged batteries, shortened battery life, and getting caught without power at the worst moment.
What Is a Battery Shunt?
A battery shunt is a precision low-resistance resistor installed in the negative cable of your battery bank. Every amp flowing in or out passes through it. By measuring the tiny voltage drop across the shunt, the monitor calculates current flow — and by integrating that over time, it tracks how much energy has entered and left the battery.
This gives you a true state of charge percentage, not a voltage reading. A 12.6V reading looks like "fully charged" but under a 40A load, 12.6V might mean 60% charged. Voltage is a poor proxy for SOC. Current integration (what a shunt does) is accurate.
Smart Shunt vs BMV-712: Which One?
Smart Shunt (the more affordable option): The shunt hardware plus Bluetooth. No display. Monitor via VictronConnect app or a Cerbo GX. Note that the base SmartShunt does not include a programmable relay.
BMV-712 Smart (a step up in price): Same shunt hardware and Bluetooth, plus a round wall-mounted display with buttons for direct readout of SOC, voltage, current, and time-to-go. The BMV-712 also includes a programmable relay, which can be configured to switch a circuit based on parameters such as state of charge or voltage.
Which to choose: If your system has a Cerbo GX, the Smart Shunt is the right choice — you don't need a second display. For most camper/RV owners without a Cerbo GX, the BMV-712 is more practical. Having the SOC visible on the wall without unlocking your phone is genuinely convenient, and the built-in relay adds flexibility for automatically controlling a load.
Installation
Straightforward: disconnect the battery, install the shunt in series with the negative cable (between the battery negative terminal and the rest of the negative bus), connect the signal wires, pair with VictronConnect, configure your battery capacity. Takes 30–45 minutes.
Critical: every load and every charging source must be on the bus side of the shunt, not directly on the battery terminal. If a wire bypasses the shunt, the monitor won't count that current and SOC readings will drift.
Real-World Use
In typical RV use with an AGM bank:
- Tracks state of charge accurately once synchronised with a full charge
- Bluetooth provides convenient monitoring at typical in-cabin distances
- SOC readings can drift over time if the battery isn't regularly fully charged — corrected by a periodic full charge to resynchronise
- On the BMV-712, the programmable relay can be configured to switch a circuit (for example a secondary fridge) at a set state of charge
Verdict
The best battery monitor for serious RV and off-grid use. Accurate, well-supported, and integrates perfectly with the broader Victron ecosystem.
Buy the Smart Shunt if you have or plan a Cerbo GX system. Buy the BMV-712 if you want a panel-mounted display without a separate screen. Either way, you're getting the most accurate and practical battery monitoring available for 12V systems.
Shop Victron Smart Shunt and BMV-712 at RV Parts Giant.