Victron MultiPlus 12/3000 keeps dropping to float too early — anyone else?

Picked up a MultiPlus 12/3000/120 last autumn for the boat. Brilliant bit of kit overall but I've got a niggle that's doing my nut in. Running 400Ah of Fogstar Drift LiFePO4, and the charger keeps hitting float when the batteries are sitting around 90-92% according to the BMS. Absorption time is set to 4 hours in VictronConnect but it's cutting short every single time.

Pretty sure it's the "tail current" setting doing it — looks like it's defaulting to 4% and the bank hits that threshold before absorption's done. I've knocked it down to 1% as a test and it's behaving better, but not perfect.

Anyone running a similar setup who's dialled this in properly? What are your absorption voltage and tail current settings for Fogstar cells specifically? I'm using 14.2V absorption, 13.5V float, which Fogstar themselves suggested — but I'm starting to wonder if their recommended charge profile plays nicely with how Victron handles the absorption cutoff logic.

Also open to the idea I've just got something fundamentally wrong in the config. Wouldn't be the first time. 🙄

Reply by JoeFox55:

@GrumpySparky — classic one this. Worth checking your absorption time settings in VictronConnect. With LiFePO4 the default absorption period is often set far too long or the "tail current" threshold is triggering float early because LiFePO4 accepts charge so efficiently it hits that cutoff quickly. That's actually correct behaviour — the battery genuinely is nearly full!

Jump into VictronConnect, go to the charger settings, and look at your tail current percentage. LiFePO4 typically wants something around 2-4% of battery capacity. For 400Ah that's roughly 8-16A. If it's set higher it'll drop to float prematurely.

Also double-check your charge voltage is set to 14.2-14.6V rather than the AGM default. Fogstar's own documentation should have the recommended parameters. What firmware version are you running?

@GrumpySparky same setup on my boat — MultiPlus 12/3000 with Fogstar Drift 200Ah cells.

The culprit for me was the adaptive absorption algorithm. Victron's default assumes lead-acid behaviour, so it shortens absorption time based on previous charge cycles. Works great for AGM, useless for LiFePO4.

In VictronConnect, go into the charger settings and switch to fixed absorption time rather than adaptive. I run 1 hour fixed at 14.2V. Also double-check your tail current setting — if it's set too high it'll trigger float prematurely before the cells are actually full.

What BMS are you running? If it's communicating via VE.Direct or DVCC, that can also interfere with the charge profile in unexpected ways.

Had this exact drama with mine at the cabin. Once you've sorted the absorption settings like @JoeFox55 says, also check your battery capacity setting in VE.Configure — if it thinks you've got less Ah than you actually do, it'll cut absorption short based on time calculations.

Also worth connecting a SmartShunt if you haven't already. The MultiPlus charging blind without proper SOC data will always make dodgy decisions. Night and day difference on mine once I got the two talking over VE.Smart networking.

One more thing — Fogstar Drift cells need the charge voltage set bang on 14.2V absorption, no higher. Some people accidentally leave it at AGM defaults (14.7V) which can confuse the tail current detection.

Reply by Wayne1978:

@GrumpySparky one thing nobody's mentioned yet — have you got a proper battery temperature sensor fitted? The MultiPlus can get a bit conservative and cut absorption short if it's making assumptions about battery temp, especially on a boat where things can get chilly overnight. The MPPT temp sensor or the VE.Bus BMS integration makes a real difference to how the charger behaves through the charge curve.

Also worth double-checking your battery capacity setting in VictronConnect is set correctly to 400Ah — if it's underestimated it'll calculate a shorter absorption period than you actually need. Easy one to overlook if you've ever reset the unit or updated firmware.

The Fogstar Drift cells are decent kit, so it's almost certainly a settings/comms issue rather than anything wrong with the batteries themselves.

Reply by JackeryFan:

@GrumpySparky worth checking your charge current setting as well. If the MultiPlus is set to a fairly low charge current relative to your 400Ah bank, it'll hit the absorption voltage threshold quicker and the tail current cutoff kicks in sooner than you'd expect — making it look like it's dropping to float prematurely when actually it's behaving correctly for those settings.

In VictronConnect (or VE.Configure if you're on a laptop), have a look at your "tail current" percentage — that's the current level at which it decides absorption is done. Default is often 4% but with LiFePO4 some folks drop it to 2% or even lower to let it properly top up.

Between that, @Wayne1978's temperature sensor suggestion, and sorting absorption voltage, you should crack it. 👍

Great shout from @JackeryFan on the charge current — that ties into something I hit during my van build. On LiFePO4 the absorption time in VE.Configure is the real culprit more often than the current setting alone. Mine was defaulting to voltage-triggered absorption exit, which on a Fogstar pack meant it was bailing out after barely 10 minutes because the cells hold voltage so flat.

Crack open VE.Configure, go to the charger tab, and switch absorption from adaptive to a fixed duration — I run 2 hours on my 200Ah setup. Also make sure your absorption voltage isn't creeping above 14.2V; Fogstar's own docs suggest 14.2V max for the Drift cells.

Once I sorted those two things together the profile actually completed properly rather than ghosting into float halfway through.

@GrumpySparky had almost this exact saga on my boat last year. The culprit turned out to be the absorption time being set far too short in VE.Configure — Victron's defaults assume flooded lead acid and LiFePO4 just laughs at them.

Crack open VE.Configure, head to the charger tab, and set absorption time to adaptive with a fixed tail current rather than a fixed timer. Once I matched the tail current to Fogstar's spec sheet (around 0.05C), the MultiPlus stopped bailing out early like it had somewhere better to be. Night and day difference.

@GrumpySparky don't overlook the BMS communication side — if your Fogstar Drift has a VE.Bus or CAN BUS port gathering dust, plugging it into the Cerbo/CCGX lets the battery tell the MultiPlus exactly when it's actually full rather than the charger just guessing like my mate Dave does at the pub quiz.

Reply by Tango65:

@GrumpySparky one thing worth looking at is your tail current setting in VEConfigure. By default it's often set around 4% of battery capacity, which on LiFePO4 can trigger the float transition far too early because these cells absorb current so differently to lead-acid near the top. Drop it down to 1-2% and see if that makes a difference. Also double-check your absorption voltage is actually set to what Fogstar recommend — I've seen MultiPlus units come preconfigured with lead-acid defaults straight out the box.

@GrumpySparky classic Victron behaviour — it's basically decided your batteries are fine actually, thank you very much, and it's going for a lie down whether you like it or not 😄

Seriously though, on top of what the others have said, double-check your battery capacity setting in VEConfigure. If it thinks you've

Reply by ShortCircuit56:

@GrumpySparky worth checking your battery temperature sensor situation as well. If the MultiPlus thinks the battery is warmer than it actually is, it'll cut absorption short as a protection measure. Had this on a camper van build — the sensor was routed too close to the alternator and was reading artificially high. Also double-check your battery capacity setting in VEConfigure matches your actual 400Ah — undersetting it means the charger calculates absorption time based on a smaller bank and bails out early. Both are easy wins before diving into anything more complicated.