Victron MultiPlus 12/3000 keeps dropping to float at 80% – anyone else had this?

Right, so here's the thing. I've been running a MultiPlus 12/3000/120-50 in the van for about eight months now, paired with three 200Ah Fogstar Drift LiFePO4 batteries (so 600Ah total at 12V). Most of the time it's brilliant. But lately — and this started maybe six weeks ago — the unit is cutting to float when the batteries are sitting around 80% according to the BMS. Not 95%, not 100%. Eighty percent.

I've checked the absorption voltage and it's set to 14.2V, which is what Fogstar recommend. The float is at 13.5V. The issue seems to happen particularly when I'm running it off shore power at a campsite, less so when it's solar-charging through the MPPT. I updated to the latest firmware last month thinking that might sort it, but no joy.

What's confusing me is the VictronConnect logs. The charger thinks it's hit absorption and timed out, but the SOC on the Cerbo GX is clearly showing 78–82% when it drops. I've got the tail current set to 4A, which should be roughly 0.5–1% of my bank capacity — maybe that's too aggressive?

Has anyone actually wrestled with the MultiPlus absorption settings on a LiFePO4 bank this size? Getting a bit fed up of starting generator runs at 3am because the van's drained overnight from an already-partial charge.

@GafferTapeKing had almost the exact same thing on my motorhome last winter. Turned out my absorption voltage was set too low — Victron was hitting the target voltage too quickly and assuming the bank was full.

Worth checking in VictronConnect:

• Absorption voltage at 14.2V for LiFePO4
• Absorption time — try 1hr minimum
• Make sure "adaptive absorption" is off if you're using lithium

Also double-check your battery's own BMS isn't sending a charge-complete signal early via any shared comms. The Fogstar Drifts don't have built-in Victron comms IIRC so probably not the issue, but worth ruling out.

What's your current absorption voltage set to?

@GafferTapeKing worth checking your battery capacity setting in VE.Configure – if it's set too low, the MultiPlus calculates charge current relative to that figure and can trigger the float transition prematurely. With 600Ah of Fogstar you want that set correctly.

Also, have a look at your tail current setting. On LiFePO4 this is usually best set around 2-4% of capacity (so roughly 12-24A on your bank). If it's left at the Victron default which is more suited to lead acid, it can end the absorption phase far too early when the batteries are genuinely only at 80%.

Pop VE.Connect on your phone via Bluetooth and watch the charge current live during absorption – that'll tell you pretty quickly whether the tail current threshold is the culprit. Sorted mine in about ten minutes once I knew what to look for.

Good shout from @Ian1968 and @CornishCamper, but just to add something different – check your tail current setting in VE.Configure. With LiFePO4, the charge current drops off quite sharply near full and if your tail current threshold is set too high (say 4-5% of capacity), the MultiPlus will interpret that natural taper as "job done" and flip to float well before you're actually at 100%.

For your 600Ah bank I'd suggest setting it somewhere around 6-10A maximum. Also worth double-checking what SOC your BMS is actually reporting via Bluetooth – the Fogstar app can sometimes tell a different story to what VictronConnect thinks is happening.

What firmware version are you running on the MultiPlus? There were a few quirks with earlier versions that affected this behaviour.

@Lee1963 has it — tail current is almost certainly your culprit, but also worth double-checking your BMS comms if you've got the VE.Bus BMS wired in, because mine on the static was overriding the MultiPlus absorption cycle entirely and calling float early like it was auditioning for a role in a disaster film.

Great points from everyone above. Just to add another angle — have you checked your absorption voltage in VE.Configure? If it's set a touch low for LiFePO4 (should typically be around 14.2–14.4V for 12V), the charger might be hitting that ceiling sooner than expected and interpreting the situation as the battery being fuller than it actually is.

Also worth having a look at your battery temperature — if you've got the temp sensor fitted and it's reading warm, the MultiPlus will compensate by backing off the charge voltage early. Had something similar on my own setup last winter.

What does the battery voltage actually read when it drops to float? That'd help narrow it down a fair bit. 🔧

Great thread, lots of solid advice already. One thing nobody's mentioned yet — have you checked your battery temperature? The MultiPlus has built-in temperature compensation that will lower the absorption voltage threshold if it thinks the batteries are warm, which can cause it to drop to float earlier than expected. If you're not using a Battery Temperature Sensor (BTS), it's just assuming ambient, which may be inaccurate especially in a van in summer. Worth grabbing one if you haven't already, they're only a few quid.

Also, @GafferTapeKing — what's your absorption time set to? If you're on a fixed time rather than adaptive, a short absorption period combined with the tail current kicking in could be compounding the issue.