Victron MultiPlus keeps switching to float too early — anyone else had this?

Had exactly this on my garden office setup last winter. MultiPlus-II 48/3000 was dropping into float at around 85-90% SOC, which was obviously nonsense. Batteries weren't fully charged but the unit thought they were.

Turned out to be a combination of two things:

1. Absorption voltage set too low — I'd copied settings from a forum post that were a bit conservative. Bumped it up to the correct figure for my Fogstar Drift cells (per their spec sheet) and it helped immediately.
2. Absorption time — had it on the adaptive setting, which was making decisions based on dodgy historical data. Switched to a fixed absorption time and it sorted itself out within a few cycles.

Worth checking your battery temperature compensation settings too if you're running lead-acid or LiFePO4 without a BMS that talks to the Victron directly. In winter the MultiPlus can misread where the battery actually is in the charge cycle.

Also — are you monitoring via Cerbo GX or just the front panel? The VictronConnect graphs were invaluable for diagnosing mine. You can see exactly where the voltage is sitting when it decides to transition to float.

What battery chemistry are you running? Settings that work perfectly for one setup can be completely wrong for another. Would be useful to know your absorption target voltage and what your current adaptive time is set to before anyone starts suggesting fixes.

Wez1993 | 847 posts

@BoxerProject classic symptom of the absorption voltage being set too low, or more likely your absorption time is too short. The MultiPlus uses a combination of voltage AND time to determine when to transition — if your battery internal resistance is a bit higher (especially in cold weather), it'll hit the target voltage quicker but without actually being full.

Worth checking your absorption time setting in VEConfigure. I'd also look at whether you've got temperature compensation enabled — without it, the charger doesn't account for the fact that batteries need higher charge voltages when it's cold. My garden office setup had similar grief last January before I sorted the temp comp properly.

What battery chemistry are you running? LiFePO4 with a BMS can also sometimes confuse the MultiPlus if communication isn't set up right.

BoatPaddy | 1,204 posts

@BoxerProject had the exact same faff on my shepherd's hut build — turned out my battery temperature sensor wasn't seated properly, so the Victron was compensating for a phantom "warm" battery and cutting absorption short like a pessimistic accountant 🔋

Check your VE.Bus BMS comms if you're running Fogstar or similar smart cells — sometimes the BMS is telling the MultiPlus it's full when it genuinely isn't, usually a cell balance issue rather than anything wrong with the charger itself.

Also worth jumping into VictronConnect and checking your absorption time minimum setting — if it's set to 0, the unit will exit on voltage alone rather than holding for a proper duration. Bumped mine to 2 hours minimum and never looked back.

WattEd | 2,341 posts

Worth checking your tail current setting in VEConfigure — this is often the culprit people overlook after sorting absorption voltage. The MultiPlus drops to float when charge current falls below a percentage of battery capacity (default is 4% of the Charger Max Current setting, if I recall correctly). If your C-rating or actual capacity is mismatched to what the charger thinks it's working with, it'll terminate absorption prematurely every time.

On my shepherd's hut LiFePO4 bank I had to drop tail current right down to 1-2% before it would properly complete the charge cycle. Fogstar Drift cells in particular seem to absorb quite slowly toward the top end.

Also — are you on the latest firmware? There were some known charging algorithm quirks in older MultiPlus-II builds that Victron quietly resolved.

WelshVanLifer | 23 posts

Had something similar on my boat's 12V system — not a MultiPlus but same principle. Once I sorted the battery temperature sensor placement it made a massive difference. Is your BMS actually communicating with the MultiPlus via VE.Bus or are they running independently? If the MultiPlus has no BMS data it'll just be guessing SOC based on voltage alone, which is notoriously unreliable especially if your cables have any meaningful resistance causing a slight voltage rise at the charger terminals. What batteries are you running — lithium or AGM? With lithium the absorption window is much shorter anyway so even a small voltage calibration error can make it bail out early.