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

Had this exact issue on my narrowboat last winter. The Multiplus was calling float after maybe 45 minutes when the batteries were nowhere near full — I could see the SOC sitting at around 68% on the Cerbo but it was already backing off the charge current.

Turned out my absorption voltage was set a touch low (around 14.0V for a 12V system) and the tail current threshold was way too aggressive. Victron's default tail current for ending absorption is something like 2A, which on a larger bank can trigger float far too early.

A few things worth checking:

• What's your battery bank size and chemistry? LiFePO4 behaves very differently to AGM here
• Have you looked at the Absorption Time setting? You can set a minimum hold time rather than relying purely on tail current
• Are you using a BMV-712 or SmartShunt for battery sensing, or is the Multiplus relying on its own voltage measurement?

The last point caught me out — my battery cable runs were long enough that there was a voltage drop the Multiplus couldn't account for, so it thought absorption was done when it wasn't. Connecting proper battery sensing via VE.Smart networking sorted it immediately.

Also worth checking if you've got any Fogstar or other BMS sending signals that might be confusing the charge profile.

What firmware version are you running? There were a few quirks in older versions around float transition behaviour that I vaguely recall seeing on the Victron community forums.

Has anyone else found the adaptive absorption algorithm causing grief, or is it usually reliable in your experience?

Lisa1978 | 847 posts | ⚡ Solar & Wind

@AlexJones This is almost certainly a battery voltage spike fooling the charger into thinking absorption is complete. Classic issue with lithium banks especially, but can happen with AGMs too. Check your absorption voltage threshold in VE.Configure — if it's set too low, even a momentary voltage rise can trigger the float transition prematurely.

Also worth looking at the "tail current" setting. If your bank is oversized relative to the charger, the tail current percentage might never actually be reached properly, so the timer kicks in early instead.

What battery chemistry are you running? And have you got a BMV or SmartShunt connected? If you're not using DVCC with a proper battery monitor feeding accurate SOC data back to the Multiplus, it'll just be guessing based on voltage alone, which rarely ends well on a boat with fluctuating loads.

Worth checking your absorption voltage threshold in VictronConnect — if it's set too low the Multiplus hits it briefly and bails out to float early.

Also double-check your battery profile matches your actual chemistry. I had something similar with my Fogstar Drift LiFePO4s until I sorted the charge parameters properly. The default settings really aren't optimised for lithium out of the box.

If you're running DVCC through a Cerbo GX or similar, make sure the BMS is actually talking to the system correctly — a dodgy CAN connection can cause all sorts of weird charging behaviour.

68% SOC and dropping to float is a classic sign the voltage is being read wrong rather than a genuine full charge. Definitely fixable! 🔧

RetiredPlumber | 1,203 posts | 🔋 Static & Backup

Had this same headache on my static caravan setup. Worth checking the adaptive absorption setting — Victron's algorithm shortens absorption time based on previous charge cycles, which sounds clever until your batteries have been sitting depleted for a week and it assumes they're healthy.

In VictronConnect, look at Battery Settings > Repeated Absorption Time and Repeated Absorption Interval. If repeated absorption is disabled or set too infrequently, the charger never does a proper full cycle after deep discharges.

Also — what batteries are you running? If they're lithium with a BMS that briefly disconnects under load, the Multiplus can misread the resulting voltage spike as absorption complete. @Lisa1978 touched on that.

Set a fixed absorption time rather than adaptive as a test and see if SOC climbs properly.

Rob1963 | 2,847 posts | 🔋 Static & Van

@AlexJones — almost certainly your DVCC settings are fighting with whatever BMS is on those batteries; if you're running LiFePO4 and haven't set the correct battery type plus told the Multiplus the actual capacity in VictronConnect, it'll guess wrong every single time like a sat-nav ignoring a road closure. Also check Repeated Absorption is enabled and Absorption Time isn't set to some optimistic 1-hour figure — mine on the static was doing exactly this until I bumped it to 2hrs. Narrowboats are notoriously awful for this because your alternator and shore power are constantly arguing over who's in charge, confusing the SOC calculation further. Had the same circus with my van conversion before I wired the VE.Bus properly.

@AlexJones also worth checking whether your battery temperature sensor is actually connected properly — a floating (no pun intended) temp sensor can convince the Multiplus the pack is warmer than it is, which nudges it into float prematurely like an over-eager holiday rep trying to get you out of the pool.