Four quantities answer four different questions
Voltage, measured in volts, describes a potential difference. Current in amperes describes charge flow at a particular moment. Amp-hours count charge; watt-hours measure energy. At a calculation voltage of 12 V, 10 A corresponds to 120 W. Maintained for three hours, that is 30 Ah, or approximately 360 Wh.
A 400 Ah bank at 12 V has a nominal energy of 4,800 Wh. This is not a guaranteed usable reserve. In our example, a chosen operating window from 90% to 50% represents 160 Ah. That assumption is for calculation, not a prescription for every battery.
SOC is an estimate, not a capacity test
The SmartShunt tracks current and derives an estimated state of charge. A high SOC therefore proves neither good battery health nor actual remaining capacity. An ageing battery can reach 100% of its current capacity while delivering less endurance than when new.
Record nominal capacity, age, chemistry, model and any capacity-test result separately. A screenshot showing only a percentage is not enough to compare two days. Include time, current, voltage and active equipment.
References for this section : Victron Energy — SmartShunt, Operation §5
Understand synchronisation before changing settings
Full-charge detection combines voltage, a low tail current and a duration. Configured capacity, the Peukert exponent and charge efficiency also influence the calculation. Check parameters against the documentation for the actual equipment and battery.
Do not force the reading to 100% merely because a charger is operating. Save the original settings and history before intervention. Setting a monitor is different from setting a charger; it cannot turn an incomplete recharge into a complete one.
References for this section : Victron Energy — SmartShunt, All features and settings §7
Why an alarm may occur under load
High current demand can increase voltage drop in the battery and circuit. Cables, connections and protective devices contribute to total resistance. Voltage at an inverter can therefore differ from the reading at the battery bank. A poor connection may also generate heat.
An observation example, without diagnosing a specific fault: an alarm appears when equipment starts, disappears when it stops and returns during another power surge. This repetition warrants examination of the circuit, not an arbitrary reduction of the shutdown threshold.
References for this section : Victron Energy — Wiring Unlimited, Theory
A six-step observation method
First identify the device issuing the alarm: monitor, inverter, GX system or BMS. Their alerts do not all mean the same thing. Preserve equipment needed for navigation and safety.
Record time, voltage, current, SOC and active loads, followed by available charging sources. Inspect minimum values and history; an averaged graph can hide a short event. Reduce only non-essential loads. Compare observations under repeatable conditions and arrange an assessment of persistent abnormalities.
Prepare the installation diagram, model references, settings and readings for the technician. Do not disconnect a cable under load for an improvised test. Unusual smell, smoke, distortion or heat calls for the boat’s safety procedures and competent assistance.
When measured current does not cover the whole bank
A circuit bypassing the shunt escapes the current count. Victron documentation also identifies settings and synchronisation as causes of incorrect SOC. Wiring checks require appropriate skills and safe isolation.
To monitor a night at anchor, make matching log entries at bedtime and on waking: same units, charger status, elapsed time and unusual uses. Repeat for several nights before sizing a replacement. An isolated percentage then becomes a usable series of measurements.
References for this section : Victron Energy — SmartShunt, Troubleshooting §10.3
Interpret voltage, current and SOC together. The percentage helps planning; it replaces neither a capacity test nor a diagnosis.
Your practical checklist
Sources & documents
- Victron Energy — SmartShunt, Operation §5
Accessed 2026-11-02 - Victron Energy — SmartShunt, All features and settings §7
Accessed 2026-11-02 - Victron Energy — SmartShunt, Troubleshooting §10.3
Accessed 2026-11-02 - Victron Energy — Wiring Unlimited, Theory
Accessed 2026-11-02
