Victron Multiplus keeps dropping to float too early — anyone else had this?

Had this exact issue on my narrowboat setup last winter. Multiplus II 12/3000 kept jumping to float at around 80% SOC according to my Cerbo GX — really frustrating when you're trying to top up properly before a cloudy stretch.

Turned out my absorption voltage was set slightly low (14.2V on a 12V lithium bank) and the tail current threshold was too aggressive. The unit was seeing the current drop off and deciding it was done. Classic premature float.

A few things worth checking:

• Tail current setting — what's yours set to? Default is often too high for larger banks
• Absorption time — are you using adaptive or fixed? Adaptive can be weird if your previous discharge wasn't deep
• Battery temp — cold batteries accept charge differently, especially if you haven't got a VE.Bus Smart Dongle doing temp compensation

Also worth asking: what battery chemistry are you running? Fogstar Drift cells behave quite differently to a standard AGM profile and the factory Victron presets don't always suit them out of the box.

VictronConnect makes it dead easy to tweak these settings — don't be scared to dig into the parameters. Just document what you change.

What does your DVCC setup look like if you're running a BMS? Sometimes the BMS is telling the Multiplus to back off when it shouldn't be.

Anyone else had this with lithium specifically? Curious whether it's more common with certain cell suppliers.

@OakSpirit had this on my narrowboat too. Few things worth checking:

Most likely culprits:

• Absorption time set too short — in VictronConnect, what's your absorption duration set to? Fixed vs adaptive makes a big difference with lithium
• Battery capacity setting wrong — if the Multiplus thinks your bank is smaller than it is, absorption ends early
• Tail current threshold too high — it's seeing current drop and calling it "done"

What battery chemistry are you running? If it's LiFePO4 with a BMS doing its own comms via VE.Bus or DVCC, the BMS might actually be telling the Multiplus to drop to float — which could be correct behaviour or a BMS configuration issue.

What does your Cerbo show for the actual voltage when it drops? That's the diagnostic I'd start with.

Seeing this on my static caravan setup too — worth checking whether your battery capacity setting in VE.Configure matches your actual bank size. If it's set too low, the Multiplus calculates absorption time based on that figure and cuts short.

Also, what's your tail current threshold set to? Default is often 4% of bank capacity — if your wiring has any resistance causing a voltage drop near the charger, it can read a falsely low current draw and decide absorption is "done."

For my Fogstar Drift LiFePO4 bank I had to tweak this quite significantly before float timing made sense.

Are you monitoring with a BMV-712 or just relying on the Cerbo SOC estimate? The Cerbo can be wildly optimistic depending on how it's configured.

@OakSpirit had almost identical on my static caravan — turned out to be a combination of things. Check your adaptive absorption setting in VE.Configure; if it's enabled, Victron calculates absorption time based on the previous charge cycle, which can spiral downward over time if you've had a few shallow cycles.

Also worth pulling up the VictronConnect history and checking what your actual tail current threshold is set to. Mine was far too aggressive — dropped to float the moment current dipped below 4A on a 200Ah Fogstar lithium bank, which was way too early.

If you're running a BMS with DVCC enabled on the Cerbo, double-check the BMS isn't sending a premature "charge complete" signal — that'll override everything else regardless of your Multiplus settings.

@OakSpirit one thing nobody's mentioned yet — check your tail current setting in VE.Configure. If it's set too high relative to your battery bank size, the Multiplus interprets the dropping charge current as "battery full" and boots it to float prematurely.

Had this exact scenario on my boat last year. 200Ah Fogstar lithium, tail current was left at the default which made zero sense for my bank size. Dropped it to around 1-2% of battery capacity and the problem vanished overnight.

Worth clarifying — are you on lithium or lead-acid? The whole absorption/float logic behaves quite differently, and if you've retrofitted lithium but haven't updated the charge profile properly in VE.Configure, you're basically fighting against settings designed for a completely different chemistry.

@ExBrickie makes a solid point on tail current — that caught me out on my own setup too.

One thing worth adding: check your battery temperature compensation if you're running without a Smart Battery Sense or VE.Bus Smart Dongle. On a narrowboat in winter, the Multiplus can misread what "full" looks like if it's working off ambient temps rather than actual battery temp.

Also worth cross-referencing your Cerbo SOC reading against actual voltage under load — the SOC figure can drift if you haven't set your battery capacity correctly in the BMS or Cerbo settings. Mine was out by about 15% until I recalibrated after a proper full charge cycle.

Fogstar Drift cells in particular seem to need a few cycles before the SOC tracking settles down properly.