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

Had this exact issue last winter with my Multiplus-II 48/3000. Was seeing it drop to float at around 80–85% SOC, which was driving me nuts — especially when I'm trying to get a full charge before a run of overcast days.

After a fair bit of digging, the culprits for me were:

• Absorption voltage set too low — I had it at 56.8V for my Fogstar Drift LiFePO4 bank, bumped it to 57.6V and it made a noticeable difference
• Absorption time — I was using "adaptive" absorption, which can be very aggressive about cutting to float if it thinks the battery is full based on tail current
• Battery monitor calibration — my BMV-712 SOC was drifting, so the system thought it was fuller than it was

The fix that worked best for me was switching to a fixed absorption time (around 2 hours) and making sure the tail current threshold in the DVCC settings was appropriate for my bank size. The default 1A tail current is comically low for larger banks.

Worth checking whether you've got a BMS talking to the Cerbo via CAN-bus as well — if your BMS is broadcasting a charge current limit that's dropping off, the Multiplus will follow it down and tip into float prematurely. Victron's documentation on this is a bit sparse.

What battery chemistry are you running and what does your VEConfigure absorption time look like? That'd narrow it down considerably.

@ThistleTel classic absorption timeout issue. Your absorption time is almost certainly set too short for your battery bank size. In VE.Configure, check your repeated absorption time and absorption repeat interval — if you've got a large Fogstar or EVE cell bank, the default settings are woefully inadequate.

Also worth checking your tail current setting. If it's set too high (say 4–5% of C), the Multiplus will exit absorption prematurely thinking the battery is full when it isn't.

My setup on the island uses 280Ah EVE cells and I had identical behaviour until I dropped tail current to 1% and extended absorption time to 3 hours. Made an immediate difference.

Run the Battery Monitor in VRM and watch the actual charge current during absorption — if it's still declining steeply when float kicks in, that confirms the timeout is your culprit.

Good shout from @IslandVanLifer on the absorption timeout, but worth also checking your absorption voltage threshold itself. If it's set too low, the Multiplus can think the batteries are fuller than they are and bail out early. On my setup I had to bump absorption voltage up slightly and also check the tail current setting in VEConfigure — that's the one that often catches people out. When current drops below that tail current threshold, it triggers the float transition regardless of your timer. Might be worth connecting via VE.Bus Smart Dongle so you can watch what's actually happening in real time rather than guessing. What battery chemistry are you running @ThistleTel? Settings vary quite a bit between lithium and lead-acid.

@ThistleTel had this exact faff with my motorhome setup — turned out my battery temperature sensor was reading high because it was mounted too close to the cells, so the Multiplus thought the pack was warmer than it was and throttled absorption early via the temp compensation curve.

Check your VEConfigure → Charger tab → Temperature compensation setting (mV/°C/cell) — if it's too aggressive and your sensor placement is dodgy, it'll bail on absorption prematurely every time.

Also worth cross-referencing your actual SOC in VRM against what the unit thinks it's doing — sometimes the state machine just needs a proper recalibration cycle (full discharge to low, then uninterrupted charge) to sort its head out.

Fogstar Drift cells in particular can be fussy about this if you've not nailed the charge parameters to the manufacturer spec.

@ThistleTel worth checking your tail current setting in VictronConnect — this is often the culprit that gets overlooked once the absorption timeout and voltage threshold have been ruled out.

The Multiplus will drop to float early if the tail current (the charge termination threshold) is set too high relative to your battery capacity. On my 200Ah Fogstar Drift LiFePO4 bank the default Victron value was way too aggressive — I had to drop it from around 4% to roughly 1–2% of C20 capacity before it stopped cutting out prematurely.

Navigate to Charger settings in VictronConnect, then look under the absorption end trigger options. If you're running lithium, also confirm your BMS isn't signalling charge complete early via DVCC — that can override everything else entirely and makes the tail current adjustment pointless until you address it upstream.

@OldSparky52 that's a really useful one — hadn't even considered the tail current setting before.

Quick question for anyone: does the tail current threshold interact differently depending on your battery chemistry? I'm running LiFePO4 cells (Fogstar Drift 100Ah units) in my shepherd's hut build and I've read that lithium wants a much lower tail current percentage than AGM — something like 2–3% vs 5%+ for lead acid.

Could an incorrectly set tail current essentially trick the Multiplus into thinking absorption is "done" prematurely if it's calibrated for the wrong chemistry? Trying to understand whether this might be my issue too, as I'm occasionally seeing similar behaviour on cloudy days when the solar isn't pushing much current through anyway.