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

Had exactly this on my Multiplus-II 48/3000 last summer. It was dropping to float after maybe 45 minutes of bulk charging, well short of what the battery needed.

Turned out to be a combination of two things:

1. Tail current set too high. VEConfigure had it at the default 4% and my Fogstar Drift 48V lithium cells were hitting that threshold far earlier than expected under the load profile I run for the garden office. Dropping it to 1% sorted the premature float issue almost entirely.

2. Temperature compensation. I had a MultiTemp sensor installed but hadn't properly calibrated the absorption voltage against the actual battery BMS limits. The Multiplus was effectively backing off voltage too soon on warmer days.

Worth checking your charge algorithm settings in VEConfigure carefully — the defaults are fairly conservative and don't always suit lithium setups. If you're running lead-acid it's a different story, but either way the tail current percentage is the first thing I'd look at.

Also double-check whether you have a DVCC setup via Cerbo or similar. If the BMS is communicating charge current limits back to the Multiplus, it can cause the tail current threshold to be hit earlier than you'd expect, particularly if the BMS gets cautious under temperature or state-of-charge conditions.

What battery chemistry are you running and do you have a Cerbo/GX device in the loop? That'll narrow it down considerably. Others here will likely have encountered the same — it's a fairly common tuning issue rather than a fault as such.

@CarlBaker curious whether your temperature sensor was doing anything odd at the time? I had a similar saga with my shepherd's hut setup — Multiplus-II 48/5000 paired with Fogstar Drift lithium cells — and it turned out the BMS was sending a false "battery full" signal over the VE.Bus because of a dodgy cell voltage reading on one group.

The Multiplus was just doing what it was told, bless it.

Worth connecting via VE.Configure and logging the charge state transitions properly rather than just eyeballing the LEDs. Once I could see the actual voltage curves, the culprit was obvious within minutes. The bulk-to-absorption threshold was being hit artificially early because one cell was reading high.

Swap out any dodgy comms cables first — I've lost hours to a slightly corroded RJ45 before now.

@CarlBaker seen this exact thing on my boat setup. Worth checking your absorption voltage threshold — if it's set even slightly low, the Multiplus thinks it's "done" way too early.

Also double-check your battery capacity setting in VEConfigure. If it's under-specified, the tail current cutoff kicks in prematurely. Caught me out when I first set mine up for the EV charging side of things.

@QuietMaker the temp sensor angle is worth pursuing too — a dodgy reading can fool it into thinking the battery is warmer than it is and back off early.

Victron's VRM logs are your friend here, can see exactly what triggered the float transition.

@CarlBaker had this on my narrowboat last year with a Multiplus-II 24/3000. Turned out my tail current setting was way too high — it was seeing the current drop to that threshold and assuming the batteries were full, even though they weren't.

Worth checking in VE.Configure under the charger tab. Default tail current is something like 4% of capacity but if your battery manufacturer specifies different (Fogstar drift cells for example want a lower figure), you can end up cutting absorption short by a significant margin.

Also double-check your absorption time isn't set to adaptive mode when your usage pattern doesn't suit it — fixed absorption time gave me much more predictable results once I'd dialled in the right duration for my bank size.

Great thread — @CarlBaker, one thing nobody's mentioned yet is checking whether you've got multiple charge sources feeding in simultaneously. I had my Multiplus dropping to float embarrassingly early until I realised my MPPT was already pushing the battery voltage up before bulk even properly kicked off. The Multiplus was essentially "seeing" a battery that looked nearly full from the moment it started.

Worth logging your battery voltage and current through a full charge cycle if you can — VictronConnect makes this fairly straightforward. That data will tell you pretty quickly whether the issue is the Multiplus misreading state of charge or something upstream skewing the voltage readings.

Also worth double-checking your wiring to the battery sense terminals if you're using them — a poor connection there can give the charger a false high voltage reading.