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

Been having exactly this issue with my Multiplus 12/3000 over the last few weeks — bulk phase barely lasts 20 minutes even when the batteries are clearly not full. Running a 200Ah Fogstar Drift lithium setup in my garden office and it's driving me mad.

I've been going back and forth on whether it's a BMS communication issue or something in the charge profile settings. The Fogstar has its own BMS obviously, but I've got it connected via VE.Bus to my Cerbo GX — wondering if the BMS is sending a premature "I'm full" signal and the Multiplus is just obediently following orders?

A couple of things I've tried so far:

• Adjusted the absorption voltage up slightly (was at 14.2V, bumped to 14.4V)
• Checked the tail current settings in VictronConnect — had it set at 4% which might have been triggering float too aggressively
• Disabled DVRS temporarily to rule out external interference

None of it's made a massive difference if I'm honest. State of charge in VRM still shows around 70-75% when it decides to drop to float, which obviously isn't right.

Has anyone with a similar lithium/Victron combo cracked this? I know Victron's lithium profiles can be a bit fussy and I suspect there's a setting buried somewhere in VEConfigure that I've not touched yet. Would love to know if this is a known quirk with Fogstar batteries specifically or whether it's more of a general Multiplus thing.

Had this exact headache with my setup last year. Nine times out of ten it's the absorption voltage threshold set too low — Victron's defaults are often configured for AGM so they bail out early on lithium.

Check your absorption voltage in VictronConnect. Should be around 14.2–14.4v for a 12v LiFePO4. If it's sitting at 14.0v or lower, the Multiplus thinks it's done when it's nowhere near.

Also — and this caught me out — make sure your tail current setting isn't too aggressive. If it's cutting to float the moment charge current drops slightly, that's your culprit.

@LiamPalmer what does your battery BMS say actual SOC is when it drops? That'll tell you straight away if the charger's lying to itself.

@LiamPalmer — this happened to me when I first commissioned my tiny house system. Turned out my battery BMS was sending a "charge complete" signal via the VE.Bus before the cells were genuinely balanced. Worth checking whether your Fogstar has a DVCC communication cable running to the Cerbo or MPPT — if it does, the BMS is essentially telling the Multiplus to stand down early, regardless of what your voltage settings say.

Head into VictronConnect, pull up the charge history and look at the actual current when it dropped to float. If it cut out at, say, 15A rather than your tail current threshold, the BMS is almost certainly the culprit rather than any misconfiguration on the Victron side.

@LiamPalmer — worth checking your battery capacity setting in VEConfigure. I had my Multiplus doing exactly this on my van build last spring, and the culprit was the "configured battery capacity" being set way too low. The charger was calculating it had reached absorption based on a fraction of the actual 200Ah bank I had.

Also, if you've got a BMV-712 or similar shunt in the loop, make sure the charge detection threshold isn't fighting the Multiplus's own assumptions about state of charge. Mine was essentially telling the charger the bank was already at 95% when it absolutely wasn't.

Download VEConfigure, connect via MK3-USB interface, and post a screenshot of your charger tab settings — the community here can spot the problem in seconds once we can see the actual numbers.

@LiamPalmer — one thing nobody's mentioned yet: are you charging from solar or shore power? I ask because I had a similar issue where my MPPT was feeding just enough current to trick the Multiplus into thinking bulk was nearly done. The charger sees rising voltage from the solar contribution and jumps to absorption prematurely.

Worth logging via VRM if you haven't already — even just a few hours of data usually makes the culprit obvious. What does your actual charge current look like during bulk? If it's dropping off earlier than expected, that'd point toward @ZI_Sparks' BMS theory. If voltage is climbing suspiciously fast, could be the solar interference issue I mentioned.

What's your charge current set to in VEConfigure relative to your 200Ah Fogstar? Fogstar recommends 0.5C max I believe.

@LiamPalmer — classic one this, and I've lived it on my narrowboat setup. The culprit nobody's mentioned yet is the repeated absorption voltage threshold in VEConfigure — if the battery voltage momentarily touches your absorption setpoint during bulk (say, due to a high-resistance connection or a brief load drop), the Multiplus thinks bulk is done and skips ahead.

Check your cable connections first — even a slightly loose terminal on a Fogstar Drift will cause voltage spikes that fool the charger completely. I've seen 0.3V phantom rises from a single dodgy crimp.

Also worth checking: adaptive charging mode. If it's enabled and the Multiplus has "learned" a short absorption from previous shallow cycles, it'll keep repeating that pattern. Disable it and set a fixed absorption time while you diagnose.