Multiplus II no lights, unable to turn on

Had almost the exact same panic with my shepherd's hut setup last autumn — Multiplus II went completely dark after sitting idle on shore power for about 8 months, came back to it and absolutely nothing, not even a flicker on the LEDs.

Turned out to be a combination of things worth checking if you're in a similar boat:

• BMS disconnecting the lithium pack — my Fogstar Drift cells had drifted low enough that the BMS had tripped out entirely, which means the Multiplus sees no voltage and just... sits there looking sorry for itself
• The rocker switch on the unit itself — genuinely embarrassing how often this gets knocked during a trip
• Pre-charge resistor issue — big capacitors inside the Multiplus can cause the BMS to see a surge on reconnection and immediately disconnect again, classic catch-22

The GFCI/RCD tripping on your return is the interesting bit though — suggests something may have gone wrong before the unit went dark, possibly a ground fault developing while unattended. Worth checking your wiring hasn't had any rodent attention if it's a trailer that's been sitting outside.

On VictronConnect, can you see the unit at all via Bluetooth even with no lights? Sometimes the comms module still has enough trickle to respond even when the main board is in protection mode.

Anyone else had RCD nuisance tripping tied to a Multiplus II specifically? Wondering if there's a neutral-earth bonding relay quirk at play here — Victron's internal relay behaviour can confuse some RCDs depending on how your install is earthed.

@CamperCarl classic case of the BMS having a lie-in — if your battery pack went into deep sleep protection while the Multiplus was just ticking over on shore power, the inverter loses its DC reference and throws a sulk.

Worth trying the "wake tap" method: disconnect shore power, apply a small 12V trickle from a car battery or jump pack directly across the DC terminals for 30 seconds to nudge the BMS awake, then reconnect your main bank.

My Fogstar Drift cells did exactly this on the narrowboat after a month unattended — sorted in under five minutes once I stopped blaming Victron for everything.

Check VE.Configure for any low-voltage shutdown thresholds that may have been set aggressively too.

@ExPostie86 has the BMS angle covered, but worth ruling out something embarrassingly simple first — check the physical on/off button on the unit itself hasn't been knocked into the off position. Sounds daft but I've seen it catch people out more than once.

Also, after a long idle period, the Multiplus II's internal microcontroller can occasionally need a hard reset. Disconnect everything — shore power, battery, even the remote panel cable if you have one — wait a full 60 seconds, then reconnect battery first, shore power second. Victron's own support docs recommend this sequence specifically.

If you've got a VE.Bus cable and a laptop handy, VEConfigure will at least tell you whether the unit is responding at all, which narrows it down enormously. Dead silence usually means either a blown internal fuse or BMS lockout — both fixable, neither catastrophic.

@TracyAllen is right, embarrassingly simple stuff gets overlooked constantly.

Had this exact scenario on my static caravan last summer — everything dead, convinced myself the Multiplus had died. Spent two hours on forums before checking the fuse on the DC cable between the battery and inverter. Blown. Ten minutes and a new fuse sorted it.

Check your DC fuses before anything else. The inline fuse or fuse block on your positive battery cable is the most likely culprit if the BMS hasn't gone into sleep protection.

Also worth checking:

• Is the rotary switch on the Multiplus itself actually in the On position rather than Charger-Only?
• Any corrosion on the DC terminals after 8 months idle?

What batteries are you running? Lithium or lead-acid makes a difference to what's likely here.

Good shout from @BayTim and @TracyAllen on the basics. One thing nobody's mentioned yet — if you've ruled out the BMS sleep and the physical connections are solid, have a look at the DC fuse on the positive cable between the battery and the Multiplus. Easy to miss and often not visually blown. A multimeter across it will confirm. Also worth checking whether the unit is actually getting the minimum voltage it needs to initialise — Multiplus II won't even flicker its LEDs if DC input drops below a certain threshold. If your batteries have sagged after 8 months of no charge, they might just be too low for the inverter to wake from. A brief boost charge directly to the battery terminals (bypassing any BMS if safe to do so) sometimes gets things moving again.

@ExpertBuild what's the BMS angle then? Don't leave us hanging.

Anyway — had similar with my cabin setup. Multiplus went dark, spent an hour checking the obvious before realising the fuse on the DC cable had quietly given up. Not blown dramatically, just... failed. Continuity tested fine visually but the multimeter told a different story.

Also worth checking: the remote on/off terminals. If something's bridged those incorrectly or a wire's worked loose, the unit won't even attempt to start. Victron's wiring is picky about that.

What's your DC voltage actually reading at the inverter terminals specifically — not at the battery. Volt drop across a dodgy connection can be enough to confuse the unit into thinking there's nothing there.