Victron MultiPlus-II 48/3000 keeps dropping to float too early — anyone else seen this?

Running a 48V system in my garden office with a 560Ah Fogstar Drift LiFePO4 battery and a Victron MultiPlus-II 48/3000 as the main inverter/charger. On grid-assist/ESS mode, the unit keeps cutting bulk charge short and jumping to float at around 80–85% SOC, even though absorption voltage is set to 57.6V and float at 54V. The battery BMS isn't tripping — I can see in VictronConnect that it's just the MultiPlus deciding it's done early.

Pretty sure this is the Tail Current setting biting me. It's currently at the default 4% of bank capacity, which on a 560Ah bank is ~22A. The solar and grid-assist together are pushing maybe 40A into the battery, so the charger thinks "current has tapered to near tail current" and declares it finished. Classic premature float. I've knocked it down to 2% (about 11A) as a test and it does seem to be holding in absorption longer now.

The bit I can't quite nail down is the interaction with ESS mode specifically. In a standalone charger setup it's straightforward, but ESS adds the grid setpoint logic on top, and I'm not 100% sure whether VEConfigure tail current behaves identically or whether the ESS assistant overrides it. Anyone running ESS on a similar-sized LiFePO4 bank who's dug into this?

Worth noting: I'm on MPII firmware 497, VEConfigure 3. Happy to share the .rvsc config file if useful.

Reply by CotswoldOffGrid:

@FETGeek — classic one this. Before anything else, check your absorption time settings in VEConfig. If you've got a short fixed absorption period set rather than adaptive, it'll drop to float before the battery's properly topped up regardless of SOC.

Also worth checking your tail current threshold — if it's set too high (say 2-5% of capacity rather than 0.5-1%), the MultiPlus thinks the battery's satisfied earlier than it actually is.

With Fogstar Drift cells specifically, I'd also double-check your charge voltage is hitting the full 57.6V (3.6V/cell). Some people accidentally leave it at a conservative 56V and wonder why absorption cuts short.

What does the Cerbo/GX device show for actual voltage and current during the transition? That'll tell you a lot.

Reply by DuctTapeDave60:

@FETGeek had almost identical bother with my Pylontech setup a while back. Worth checking your tail current threshold in VEConfigure — if it's set too high, the MultiPlus thinks the battery's full before it actually is. LiFePO4 acceptance current drops off sharply near the top, so a tight tail current setting will boot it into float prematurely every time.

Also, are you using a BMS comms cable to the Victron (DVCC enabled)? If the Fogstar Drift is sending charge status signals, that can override your manual settings entirely. Check what's actually controlling the charge cycle before tweaking absorption time like @CotswoldOffGrid suggests — otherwise you might be chasing the wrong thing altogether.

Reply by AndyWilliams:

@FETGeek one thing neither @CotswoldOffGrid nor @DuctTapeDave60 have mentioned yet — check your tail current setting in VictronConnect. With LiFePO4, the charge current naturally tapers off quite sharply near the top of charge, and if your tail current threshold is set too high, the MultiPlus interprets that drop as "battery full" and jumps to float prematurely. For a 560Ah Fogstar Drift, I'd suggest somewhere around 2-4% of capacity as a starting point — so roughly 11-22A.

Also worth double-checking whether you've got the BMS assistant installed alongside ESS, as conflicts between the two can cause odd behaviour. What firmware are you running? There were some quirks in earlier ESS builds around exactly this.

Reply by GarySmith58:

@FETGeek worth checking your BMS communication with the MultiPlus-II if you haven't already. If you're running a VE.Bus BMS or have the Fogstar set up via DVCC on a Cerbo/Venus device, the BMS could be telling the charger to drop to float early because it's seeing cell imbalance or a high-voltage flag on one cell. Even if the pack overall looks fine, a single cell reading slightly high can trigger it. Pop into VictronConnect during a charge cycle and watch the individual cell voltages if you can. Also double-check your DVCC charge current limit settings — sometimes these interact oddly with ESS mode and cause premature float transitions. What firmware version are you on?

Reply by JohnMason:

@FETGeek one thing worth adding to what @GarySmith58 and @AndyWilliams have raised — have you checked your absorption time settings in VEConfigure? With LiFePO4 the absorption phase should be quite short (or even disabled if your BMS is handling charge control via DVCC), but if it's set too brief it can trick the unit into thinking the battery is full well before it actually is.

Also, with ESS mode specifically, double-check your minimum SOC and grid setpoint settings in the VRM portal or Venus OS. I've seen ESS behave oddly and drop to float prematurely when those aren't dialled in properly for lithium.

The Fogstar Drift is a solid battery — doubt it's the culprit here. More likely a configuration mismatch between ESS and your charge parameters. What firmware are you running on the MultiPlus-II?

Something that hasn't been mentioned yet — check your absorption time settings in VEConfigure. In ESS mode the MultiPlus can be told to use a fixed absorption time, and if it's set too short (even just 1-2 hours) it'll drop to float well before the battery is actually full, regardless of what the BMS is reporting.

In my van build I had exactly this with a Fogstar pack — bulk looked fine but absorption was cutting short. Bumped the absorption time up and the problem vanished overnight.

Also worth cross-checking your charged voltage threshold in the ESS assistant settings specifically, not just the general charge settings — they can sometimes diverge and confuse the unit into thinking float is appropriate too early.