Victron Multiplus keeps throwing a low battery warning but voltage looks fine on the BMV

Had almost identical on my narrowboat last winter. BMV-712 showing 12.4v, Multiplus crying about low battery every time I kicked the inverter on under any decent load.

Turned out to be a combination of two things:

1. Voltage drop under load — the BMV measures at the battery terminals, but if your cabling between the battery bank and the Multiplus isn't up to scratch, the inverter sees a much lower voltage than what the BMV is reporting. Worth checking your cable runs and connections, especially any crimps or lugs that might have a bit of corrosion on them.

2. Low battery threshold set too conservatively in VEConfigure — mine was factory default and wasn't really calibrated for my Fogstar Drift lithium cells. Dropped the DC input low shutdown by about 0.3v and the false alarms stopped.

What batteries are you running? LiFePO4 and lead-acid behave very differently under load — a lead acid at 12.4v resting can sag to 11.8v pretty quickly if you're pulling 1500W+, and the Multiplus will absolutely throw a fit.

Also worth checking — is your BMV shunt wired correctly so everything goes through it? If any loads or charge sources bypass the shunt, your state of charge figures will drift and the readings become meaningless over time.

What does the voltage actually drop to on the BMV when the warning triggers? That's the key bit of info. Would help narrow it down.

@GafferTapeKing19 classic voltage-under-load sag issue — worth checking your battery cable cross-section and connection resistance first before assuming it's a BMS or cell problem.

On my static caravan setup I had similar; BMV resting voltage looked healthy but the Multiplus was seeing a significant drop at its own terminals under load. Ran a proper voltage drop test with a clamp meter — found 0.4v disappearing across dodgy lugs on the busbar.

Key things to verify:

• Cable sizing — are you running genuine 70mm² or has someone cut corners with 35mm²?
• Torque on all terminals — Victron recommends specific torque values, they're in the manual
• Battery internal resistance — aging cells sag hard under load even if resting voltage appears fine; BMV charge cycle history will tell you a lot

The Multiplus sees inverter terminal voltage, not battery terminal voltage. That difference is everything.

Really useful thread this. I've been troubleshooting something similar on my garden office setup — Multiplus-II 24/3000 with a Fogstar Drift 24v LiFePO4.

Quick question for the group: does the Multiplus pull its low battery alarm trigger from the measured terminal voltage, or from the configured threshold in VEConfigure? Trying to understand whether the alarm fires before the BMV even registers the sag, given the BMV is sampling at a slightly different point in the circuit.

Also wondering — has anyone checked whether the Multiplus response time is the culprit? If the voltage dips briefly under load spike and recovers within seconds, would the BMV's averaging smooth that out whilst the Multiplus catches the raw peak-sag?

@PennineVanLifer your point about cable cross-section is worth stress-testing — what gauge are people running on a 24v system for a 3kW inverter?

@MuddySkipper what battery chemistry are you running in the garden office? I've got a similar setup and found the Multiplus low battery threshold settings in VE.Config can be wildly off-spec for LiFePO4 if it's still set to flooded/AGM defaults.

Worth checking what your DC input low shut-down and restart voltages are set to — they might be tripping at a voltage that's actually fine for lithium. On a 24v system especially, the numbers look different to what you'd expect coming from 12v.

Also curious what cable runs you're dealing with — longer distances between battery bank and inverter compound the sag @PennineVanLifer mentioned, even if the BMV is reading fine at the battery terminals.

@MuddySkipper worth checking your DC voltage setpoints in VE.Configure — the Multiplus-II's low battery cutoff defaults aren't always appropriate for lithium. If you're on LiFePO4, the resting voltage sits much flatter across the discharge curve so 24V on a 24V bank can look healthy at rest but sag hard under load.

Also worth looking at your Dynamic Current Limiter setting. If it's disabled, the Multiplus can demand more current than your BMS will allow in one shot, which trips the protection and the Multiplus reads that as a battery fault rather than a BMS cutoff.

Had similar grief on my static caravan setup. Ended up being a combination of undersized DC cable and the DCL setting. Once I sorted both, the warnings stopped completely.