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

Been having this exact issue with my Multiplus II 48/3000 for the past few weeks. Running a 16kWh Fogstar Drift LFP setup and the unit keeps dropping into float at around 54.2V when I've got the absorption target set to 56.8V. It's almost like it's deciding it knows better than the settings I've put in.

Checked all the obvious stuff — battery temp sensor reading correctly, no alarms on the DVCC side in VictronConnect, and the absorption time is set to a fixed 2 hours rather than adaptive. Still does it.

What's puzzling me is that it only seems to happen on cloudy days when the solar input is lower. On a bright day it charges absolutely fine and holds absorption properly. Makes me wonder if there's some interaction with the MPPT (I've got a SmartSolar 150/45) when the available current drops below a certain threshold — almost like the Multiplus is interpreting low current as "battery must be full."

Has anyone dug into the ESS settings to see if something there is overriding the charge curve? I've read that ESS mode can behave differently to Charger-Only mode but I can't find a clear explanation of why it would cut absorption short.

Also — is this worth raising directly with a Victron dealer or is it the sort of thing that gets sorted with a firmware update? My unit is on v502 at the moment.

Would be interested to know if anyone else has seen this pattern specifically on mixed solar/cloudy days, or if my setup is just doing something odd.

@Chris1966 classic symptom of the absorption time being too short, or the tail current threshold being set too high in VEConfigure.

With LFP you want to keep absorption quite short anyway, but check your tail current setting — if it's too aggressive it'll boot you into float prematurely. I'd also look at:

• Battery temperature — cold cells accept charge slower, so tail current drops off quicker
• Whether your Fogstar BMS is sending any charge limiting signals via the VE.Bus/CAN connection

Mine did similar on my static van setup until I adjusted the tail current from 4% down to 2% of battery capacity. Made a noticeable difference.

Also worth checking if the Multiplus firmware is current — there were some quirks in earlier versions around LFP charge profiles.

What charge profile are you actually running in VEConfigure?

@Chris1966 worth checking your absorption voltage setting too — if it's been drifted down slightly (common after firmware updates resetting parameters), the BMS on the Fogstar cells may be communicating a slightly lower target via DVCC, causing the Multiplus to think it's done sooner than it actually is.

In VictronConnect, navigate to ESS → DVCC settings and verify SVS (Shared Voltage Sense) is pulling the correct reference. I had almost identical behaviour with my garden office setup — turned out DVCC was reading a slightly elevated cable-voltage rather than true battery terminal voltage, making absorption appear complete prematurely.

Also double-check your Peukert exponent and charge efficiency factor in the BMV settings if you're running one — these affect how the Cerbo/GX calculates SoC, which can trigger early float transitions indirectly.

@Chris1966 really interesting one — have you checked what your tail current is actually set to in VictronConnect? On my van build with a similar LFP setup I found the default was way too aggressive, essentially telling the Multiplus the battery was full long before it actually was.

Worth connecting via VE.Configure and looking at the "tail current" percentage — what figure are you seeing there? Some people run into this after a firmware update quietly resetting values too, so worth double-checking everything against your original settings.

Also — is the BMS reporting anything unusual around that 54.2V point? Sometimes the BMS and the Multiplus aren't quite talking the same language and it's the BMS nudging the charger back rather than the Multiplus itself deciding to drop out early.

@Chris1966 had almost identical grief with my static van setup — turned out my repeated absorption setting was completely wrong, so once it hit float it'd never properly re-trigger absorption the next cycle even after a cloudy day hammered the batteries down overnight. Worth checking ESS → Scheduled Charging too if you're running ESS mode, because that can quietly override your charge curve settings in ways that'll have you pulling your hair out for weeks before you spot it in the logs.