Inverter Smart - zu wenig Spannung

Had something similar crop up on my boat setup last winter — worth sharing in case anyone else runs into this.

Running a Victron MultiPlus 12/3000 (not the Smart Inverter specifically, but close enough), and I started getting low voltage shutdowns even though the batteries were clearly fine. The VictronConnect app was showing a completely nonsensical voltage reading — nowhere near what my BMV-712 was reporting.

Turned out the issue was a dodgy connection on the sense wiring rather than the battery voltage actually being low. The inverter was reading phantom low voltage and shutting itself down as a precaution. Frustrating when you first see it, but actually the protection doing its job I suppose.

A few things worth checking if you're seeing similar:

• Battery terminal connections — corrosion is sneaky, especially on a boat
• Remote sense wires if your unit uses them — these can give wildly wrong readings if loose
• Firmware — update via VictronConnect and see if the reading stabilises
• Check whether your other Victron devices (MPPT, BMV etc.) agree on the voltage — if they do and the inverter alone is wrong, it points to a comms or sensor issue rather than actual low voltage

Mine sorted itself after cleaning terminals and re-seating connections throughout. If the app is genuinely showing 0.2V while everything else reads normal, I'd suspect a faulty internal voltage sensor or a firmware glitch before assuming the batteries are actually collapsing.

Anyone else seen inverter voltage readings drift this badly? Curious whether it's more common on certain firmware versions.

@KevWatson57 — worth checking your DC cable sizing if you haven't already. A 3000VA MultiPlus at 12V is pulling potentially 250A+ under load, and even a small amount of resistance in undersized cables will cause significant voltage drop right at the inverter terminals.

Had exactly this on my narrowboat — batteries showing 12.4V at the bank but the MultiPlus was reading 11.8V and throwing low-voltage warnings. Turned out my 70mm² cables were marginal for the run length.

Key things to verify:

• Cable cross-section relative to run length
• Crimped lugs vs. proper compression terminations
• Battery terminal connections — corrosion adds resistance invisibly
• BMS settings if you're on lithium (Fogstar Drift cells can have conservative disconnect thresholds)

Victron's MPPT calculator spreadsheet is useful for working backwards from your symptoms.

@PanelEwan's cable point is spot on but don't overlook the battery connections themselves — a slightly loose terminal on a 12V system is basically a voltage drop factory working against you, and my static van's Fogstar lithium nearly had me fooled the same way last winter before I realised the culprit was one slightly manky ring terminal doing its best impression of a resistor.

Good shout from @MoorRuss and @PanelEwan on the cabling side. One thing I'd add — worth checking your battery state of health if it's been sitting over winter. Had this exact issue on my static last year with a Fogstar Drift 200Ah. Voltages looked reasonable on the BMS display but under load from the inverter it was sagging badly. Turned out two cells had degraded.

The MultiPlus will throw low voltage warnings even if resting voltage seems fine — it's the under-load drop that catches you out.

Something nobody's mentioned yet — temperature.

Had this exact fault on my narrowboat two winters back, Victron MultiPlus throwing low voltage warnings that made no sense on paper. Turned out the battery bank was sitting in an uninsulated locker, and at 4°C a lithium battery's usable capacity absolutely tanks. The BMS was throttling discharge current to protect the cells, which looked identical to a voltage/cabling fault from the outside.

Wrapped the battery compartment in a bit of kingspan offcuts, stuck a cheap temperature sensor on it via VRM, and the warnings stopped overnight.

@Fiona1974 mentions SoC which is related — worth knowing that your battery monitor might be lying about SoC if it was calibrated at warmer temps.

Not saying this is definitely your issue @KevWatson57, boats in winter are just miserable little cold traps for batteries.