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

Had exactly this on my boat install last winter. Multiplus II 24/3000 kept jumping to float after maybe 40 minutes of bulk, batteries nowhere near full. Drove me mad.

Turned out to be a combination of two things:

1. Absorption voltage set too low — VE.Configure had it at 28.0V when my Fogstar Drift LiFePO4s needed 29.2V. Easy fix once I actually read the battery spec sheet properly.
2. Tail current threshold — this is the sneaky one. If your battery bank is undersized relative to the charger, the current naturally drops faster, and the Multiplus interprets that as "battery full" even when it isn't. My tail current was set at the default 4% which was too aggressive for my setup.

Worth checking both in VE.Configure or VE.Bus System Configurator. The interface is clunky but it's all in there.

Also — what's your battery chemistry? If you're running AGMs this is a completely different conversation. LiFePO4 profiles are much flatter and the Multiplus can get confused if you're using a generic profile rather than a custom one.

What size bank are you running against what size charger? That ratio matters more than people think.

@BrianBrown curious what the "combination of" was — post got cut off mate.

Classic culprit that often gets overlooked: tail current setting. If your absorption tail current is set too high relative to your actual battery bank capacity, the Multiplus thinks it's done when it isn't. Default Victron settings assume lead-acid — if you've swapped to lithium (Fogstar Drift or similar) you need to revisit those figures entirely.

Also worth checking:

• Battery temperature — cold batteries on a boat in winter will behave oddly
• Peukert exponent in MPPT/BMV settings if you're using a BatteryProtect or SmartShunt
• Wiring resistance causing voltage drop that fools the charger

Had similar on my cabin build. Turned out the absorption voltage was set 0.3V too low — charger thought it had reached target, bailed early. Five minutes in VictronConnect fixed it.

@BrianBrown yeah your post got cut off, dying to hear the full story!

While we wait — one classic culprit that often gets overlooked is your battery temperature sensor reading incorrectly. If Victron thinks the batteries are warmer than they actually are, it'll reduce the absorption target voltage and cut bulk short. Worth checking the sensor is making proper contact with the battery casing and not just dangling in mid-air somewhere.

Also worth having a look at your absorption time settings in VEConfigure — if you've got it set to a fixed short absorption rather than adaptive, that could easily explain 40 minutes of bulk then straight to float regardless of actual charge state.

What battery chemistry are you running? AGM, lithium, flooded? Makes a big difference to where the goalposts should be set. Victron defaults aren't always right out of the box.

@BrianBrown yes your post cut off at the worst possible moment, cheers for that.

While we're waiting — had something similar on my garden office setup with a Victron SmartSolar. Turned out my absorption voltage threshold was set too low, so the charger thought it had hit target voltage way ahead of schedule and bailed out early.

Worth checking in VE.Configure:

• What's your absorption voltage set to?
• What's your adaptive absorption setting doing?
• Are you monitoring actual battery voltage at the battery terminals rather than trusting the Multiplus measurement alone?

Cable voltage drop between charger and batteries can fool the unit into thinking voltage is higher than it actually is. Proper sense wiring sorts that.

What battery chemistry are you running? Flooded, AGM, lithium? Makes a massive difference to where these thresholds should sit.

@BrianBrown same thing happened on my static caravan setup last spring — absolute nightmare to diagnose. Mine turned out to be the battery temperature sensor giving daft readings, which was making the Multiplus think the batteries were warmer than they were and backing off the charge current early.

Worth checking in VictronConnect whether your absorption voltage is actually being reached before it drops to float, or if it's timing out. There's a configurable absorption time in there that might be set too short.

Also — are you using a BMV or SmartShunt for battery monitoring? Mine behaved completely differently once I had proper state-of-charge feedback rather than the Multiplus guessing blind.

What battery chemistry are you running? My Fogstar lithiums needed completely different charge profile settings compared to what the Multiplus defaults to out of the box.