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

Had this exact headache last winter with my van build. Multiplus 12/3000 was calling float after maybe 45 minutes even though the Fogstar Drift lithium was nowhere near full — sitting at 27.2V on a 24V system and the BMS was still showing 68% SOC.

Turned out I had the absorption voltage set too low relative to what the Fogstar actually wanted. The Multiplus was hitting its target, ticking the "job done" box, and moving on. Classic case of generic lead-acid profiles being lazily applied to lithium chemistry.

What fixed it for me:

• Bumped absorption voltage to 28.4V (matching Fogstar's recommended charge profile)
• Set a fixed absorption time of 2 hours rather than letting it use the adaptive algorithm
• Turned off the repeated absorption feature which was confusing things further

The adaptive algorithm is genuinely clever when it's calibrated right, but out of the box it can be a bit optimistic.

Worth checking in VictronConnect whether you're running the latest firmware too — there were some known quirks in earlier versions around absorption termination on lithium profiles.

One other thought: if you've got a BMV-712 or SmartShunt in the loop, make sure the charger is actually seeing SOC data via VE.Smart networking. Mine wasn't synced properly and the Multiplus was essentially flying blind.

What battery chemistry are you running? That'd help narrow it down. Others on here will probably have had similar depending on the setup.

@Gazza almost certainly a battery voltage sensing issue rather than the charger being faulty. The Multiplus is reading absorption as "done" because the tail current threshold is set for AGM defaults, not lithium.

In VictronConnect, check your charge current tail setting — on lithium it should be around 2-5% of battery capacity, but factory default is often way too high, so it hits that threshold prematurely and rolls into float.

Also worth checking whether you've got a BMV-712 or SmartShunt in the loop. If the Multiplus is relying solely on its own voltage sensing rather than battery-side data via VE.Smart networking, you'll get this constantly with lithium's flat discharge curve.

Did this exact faff sorting my garden office setup on a Fogstar Drift 200Ah. Ten minutes in VictronConnect sorted it completely.

@Gazza this is really timely — I've been lurking on this thread because I'm seeing something similar with my cabin setup. Quick question though: are you using the Victron VE.Bus Smart Dongle or relying on the built-in battery sensing? I've read that remote temperature and voltage sensing via a BMV-712 makes a massive difference to how the absorption/float transitions behave.

Also, what are your charge absorption voltage and time settings in VEConfigure? I'm wondering if the "adaptive absorption" algorithm is cutting corners based on previous cycle history rather than actual SOC. Is there a way to force a fixed absorption time instead?

Genuinely asking because I need to get this sorted before I start pulling more load for EV charging off the system — can't afford the battery sitting at 85% when I need maximum capacity.

@Gazza @GemmaWood — really glad this thread came up, I'm dealing with something similar at my cabin too. Quick question for anyone who's sorted this: is the voltage sense wiring on the Multiplus running directly to the battery terminals, or are yours tapping off the busbar? I've read that even a short cable run with undersized wire can cause enough voltage drop to confuse the charger into thinking the battery is fuller than it is.

Also worth checking — are you running the VE.Configure absorption time settings, or leaving it on adaptive? My understanding is adaptive mode can behave oddly with lithium if the battery BMS is occasionally throttling charge current mid-cycle.

Would a Victron BMV-712 with the DVCC enabled through VenusOS actually fix this properly, or is that overkill for a straightforward cabin backup setup?

@Gazza @GemmaWood this rings a bell — had almost the exact scenario with a Multiplus 24/3000 and a Fogstar Drift 200Ah last spring.

The culprit in my case was absorption voltage set too conservatively in VE.Configure. The Multiplus was hitting its absorption target, declaring victory, and dropping to float — completely ignoring the fact that current hadn't tapered down to anything meaningful yet.

Two things worth checking:

• Tail current setting — this is the real "charge complete" signal for lithium. Mine was set to the factory default (which assumes lead-acid behaviour). Bump it down to around 2–4% of capacity.
• Absorption time — set a minimum floor, not just a voltage trigger.

If you've got a Cerbo or BMV-712, the battery's own SoC reading versus what the Multiplus thinks is happening tells the whole story immediately.