Multiplus II 12/3000 stops working when cold

Had something similar happen on my boat last winter and it had me stumped for a good few hours.

Woke up to find my Multiplus refusing to do anything useful — no obvious fault codes, just... nothing. Ambient temp had dropped to about 2°C overnight in the engine bay where it's mounted. Eventually traced it back to the unit going into some kind of protection mode, though I'm still not 100% sure whether it was temperature-triggered or whether the lithium cells (Fogstar 12V 200Ah) had dipped low enough overnight that the Multiplus decided it wasn't happy.

A few things I've been wondering about since:

• Does the Multiplus II actually have a low-temperature cutoff built in, or is that purely handled by the BMS on the battery side?
• Has anyone found that mounting location makes a real difference? Mine's in a fairly exposed spot and I've been considering some kind of insulated enclosure or even a small heat mat
• Is there a VE.Connect setting I should be checking for cold weather behaviour?

Worth checking your battery voltage first obviously — if the cells dropped below ~11.5V the inverter will shut itself off before it even tries to power anything. That's probably the first thing to rule out before assuming it's the Multiplus itself playing up.

Anyone else running these through a proper UK winter aboard a boat or in a van? Curious whether this is a recurring thing or whether I just got unlucky with a particularly cold night. Also wondering if anyone's had issues with the shore power charger side of the unit behaving oddly in the cold rather than the inverter side specifically.

@WelshVanLifer classic cold weather issue this. The Multiplus II has a low temperature cutoff and if your battery bank dropped below around 5°C it'll protect itself.

Worth checking:

• VE.Configure — look at the battery temp compensation settings
• If you're running LiFePO4, most BMS units will disconnect below 0°C for charge protection anyway
• Victron's own temp sensor (if fitted) can sometimes give dodgy readings when damp

On my garden office setup I had the same drama last January. Turned out the Fogstar cells had hit 3°C overnight and the BMS just said no.

Simple fix is insulating the battery compartment. Even cheap foam board makes a massive difference. Some people run a small thermostatically controlled heat mat underneath the batteries but personally I'd sort the insulation first before adding more complexity.

@Wez1961 got cut off mid-sentence which is ironic given the thread topic

@Wez1961 the forum literally cut you off mid-sentence about cutoffs 😂 @OffGridGeek already clocked it but had to be said again.

Anyway — had this exact thing in my motorhome last January, minus temps overnight and my Victron just sat there looking useless. Turns out my Fogstar lithium

@Wez1961 finish your sentence, man! 😄

To add something useful — worth checking your battery temp sensor is actually seated properly. Mine came loose over a particularly rough patch of road last autumn and the Multiplus was reading phantom temperatures. Ended up triggering low-temp protection when the batteries were actually fine.

Also if you're running Fogstar Drift cells (or similar LiFePO4), double-check the BMS has its own cold cutoff configured correctly — sometimes you end up with two conflicting protection systems and diagnosing which one actually pulled the plug is half the battle.

VictronConnect will show you historical data in the inverter menu which can help narrow down exactly when it tripped and what it was seeing at that point.