Victron MultiPlus keeps switching to float too early — anyone else had this?

Had this exact issue on my motorhome last summer. MultiPlus was dropping to float way before the batteries were actually full — turned out my absorption voltage was set correctly but the absorption time was far too short.

Worth checking a few things:

• Absorption time — are you running adaptive or fixed? Adaptive can be a bit aggressive if your battery voltage bounces up quickly under light load
• Tail current setting — if you've got this enabled, even a small load can fool it into thinking charging is done
• Battery type config — had mine set to AGM when I'd swapped to lithium (Fogstar Drift cells), caused all sorts of odd behaviour

Sorted mine by switching to fixed absorption time and tweaking the tail current threshold in VictronConnect. Once I actually matched the settings to what Fogstar recommend, it started behaving properly.

What batteries are you running? Lithium and lead behave quite differently here and the defaults in VE.Configure aren't always sensible out of the box. Also worth checking if you've got a BMV or SmartShunt in the loop — letting the MultiPlus charge based on actual SoC rather than voltage alone made a big difference for me.

Anyone else found the adaptive absorption particularly twitchy on smaller bank sizes?

@SuffolkSolar the absorption time thing catches so many people out. On my Transit van build I had the same head-scratching moment — Victron defaults to a fairly short adaptive absorption period, and if your battery voltage climbs quickly (especially if you're running lighter loads during charging), it'll exit absorption early thinking the job's done.

Worth checking whether you're on adaptive or fixed absorption in VictronConnect. I switched mine to fixed — 2 hours for my 200Ah Fogstar Drift lithiums — and the early float nonsense stopped immediately.

Also double-check your tail current setting if you're on lithium. That's the other sneaky culprit; if it's set too high, the MultiPlus decides absorption is "complete" based on current draw rather than time.

@SuffolkSolar worth checking your tail current setting in VEConfigure if you haven't already — that's the other culprit nobody mentions. If it's set too high (say 4-5% of battery capacity), the MultiPlus decides "job done" and bails to float prematurely even when absorption time looks sensible on paper.

On my garden office setup with 200Ah of Fogstar Drift LiFePO4, I had this exact fight. The default tail current was way too aggressive for my battery bank size. Dropped it to around 1-2% and suddenly the charge cycles actually completed properly.

Also worth cross-referencing your battery BMS data against what VRM is reporting — sometimes what looks like premature float is actually the BMS quietly throttling current and fooling the MultiPlus into thinking the pack is satisfied. Two completely different problems, same symptom.

@TracyAllen — tail current was going to be my first question too, beat me to it. What value did you end up settling on for yours?

For what it's worth, I had something vaguely similar setting up my garden office system — MultiPlus was behaving oddly during absorption and I spent ages faffing with absorption time before realising my battery monitor wasn't calibrated properly. The Cerbo GX was basically lying to the charger about state of charge. Worth ruling that out @SuffolkSolar if you've got any kind of BMS or external monitor in the loop — is it talking to the MultiPlus via VE.Bus or just sitting there doing its own thing independently?

What batteries are you running? LiFePO4 with its own BMS changes the picture quite a bit compared to AGM.

@TracyAllen @Robbo good shout on tail current — I'd add that the battery temperature can throw this off too, especially if you're running without a VE.Smart temperature sensor. On my narrowboat last winter the MultiPlus was seeing ambient temps near the battery bank as warmer than reality, so it was calculating a false "full" state and bailing to float early.

Worth also double-checking your battery capacity setting in VEConfigure matches your actual bank — I'd seen installs where someone had swapped to larger Fogstar cells but never updated that figure. The algorithm uses it to calculate when absorption should reasonably end.

If you've got a BMV or SmartShunt, enable DVCC in Venus OS and let that take over charge control — made a noticeable difference on my setup.

Lived this exact nightmare on the boat last winter. Three weeks of thinking my Battle Born equivalents were getting a proper feed, only to realise the MultiPlus had been knocking off early like a builder at 3pm on a Friday.

@TracyAllen and @PennineNomad have covered tail current and temperature — both solid. What nobody's mentioned yet