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

Had this exact issue last summer with my Multiplus II on the static. Would hit absorption for maybe 20 minutes then just drop straight to float with the batteries nowhere near full — Fogstar Drift LiFePO4s showing around 80% on the BMS app.

Turned out to be a combination of two things:

1. Tail current set too high — the Multiplus was seeing the charge current drop to what it thought was "battery full" level, but that was just the BMS doing its balancing thing. Dropped the tail current percentage right down in VictronConnect and it made a massive difference.

2. Absorption time was fixed rather than adaptive — worth checking which mode you're running. Adaptive absorption adjusts based on how long bulk took, which generally gives better results with lithium.

Worth also double-checking your battery voltage thresholds are actually matched to your cells. Some of the default LiFePO4 presets in VictronConnect are a bit conservative and don't reflect what your BMS is actually happy with.

Do you have a Cerbo or any kind of GX device in the system? If so, are you running DVCC? That can sometimes cause odd behaviour if the BMS and the Multiplus are effectively fighting each other for control — had a weird week troubleshooting that before I realised DVCC was partially enabled but not properly configured.

What batteries are you running and what does your absorption voltage sit at currently? That'd help narrow it down a bit.

@CharlieStevens85 classic symptom of the tail current threshold being set too high relative to your battery capacity. In VictronConnect, check your absorption tail current — default is often 1A or 2A, which is fine for a small bank but if you've got a decent-sized Fogstar Drift setup the BMS will be pulling more than that during balancing and the Multiplus interprets it as "full" prematurely.

Try bumping the tail current up to around 4–5% of your C20 capacity as a starting point. Also worth checking whether you've got the battery preset set to lithium or if it's still on a generic AGM profile — I've seen that catch people out more than once on the static caravans I've worked on.

What's your actual battery bank size? That'll help narrow down sensible figures.

@PennineNomad has the tail current angle covered, so I'll add the other culprit I chased around my shepherd's hut setup for a fortnight before finding it — the Absorption Time setting in VEConfigure.

By default it's adaptive, which sounds clever, but with LiFePO4 it can get genuinely confused about where it is in the charge cycle. Mine was cutting absorption embarrassingly short because the previous cycle had been a shallow discharge.

Worth switching to fixed absorption time temporarily, just to isolate whether it's the tail current threshold misbehaving or the adaptive algorithm throwing a wobble. Set something sensible for your Fogstar's capacity — their own documentation gives guidance — then watch it properly for a full cycle.

Victron's adaptive mode was really designed with lead-acid in mind. LiFePO4 has a very flat voltage curve and it does tend to bamboozle it.

@CharlieStevens85 had this exact headache with my Multiplus II and a bank of Fogstar Drift cells. Once @PennineNomad's tail current fix is sorted, check your absorption voltage too — if it's set even slightly low the charger thinks it's done before it's started. Fogstar recommend 3.55V/cell minimum for bulk/absorption on the Drift chemistry, which on a 48V bank means pushing the Multiplus up to around 57.6V. Most people leave it at some conservative default and then wonder why their batteries are chronically undercharged. VictronConnect makes it straightforward enough once you've got the USB cable and stopped fighting with Bluetooth dropouts.

Great thread, this one. Just want to add something nobody's mentioned yet — have you checked your battery temperature sensor is actually doing its job properly? On my setup I found the MPTT (multi-point temperature compensation) was essentially telling the Multiplus the batteries were warmer than they were, which caused it to back off absorption prematurely as a protective measure. Worth pulling up VictronConnect and watching the live temperature readings during a charge cycle.

Also @CharlieStevens85 — are you running VE.Bus Smart Dongle or direct USB? I found remote monitoring massively helped me diagnose exactly when the drop to float was happening and correlate it with other readings. Sometimes what looks like an absorption timeout issue is actually something else entirely triggering it upstream. Happy to walk through the VE.Configure settings if you want another pair of eyes on it. 👍