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

Had this exact drama on the boat last summer. Multiplus kept declaring victory and flipping to float when the batteries were clearly nowhere near full — Fogstar lithium cells sitting at what the BMS was telling me was a measly 78% SoC.

Turned out my absorption voltage was set a touch low for the bank, so the Multiplus was hitting that target voltage quickly under reduced charge current and thinking "job done, lad." Classic premature celebration.

A few things worth checking:

• Absorption voltage — is it actually set correctly for your battery chemistry?
• Absorption time — in VEConfigure you can set a minimum absorption time, which forces it to stay in that phase even if voltage looks happy
• Tail current setting — this is the one most people miss. It's the current threshold at which the Multiplus decides absorption is finished. If it's set too high, it bails out early

On lithium especially, that tail current setting is doing a lot of the heavy lifting. Mine was left on the default which was way too generous.

Popped into VEConfigure, dropped the tail current threshold and added a 20-minute minimum absorption time, and it's been rock solid since. Batteries actually get to where they should be now before float kicks in.

What batteries are you running? That changes the answer quite a bit. Also — are you on the latest firmware? There were some quirks in older versions around this.

Anyone else had the tail current catch them out? Feels like it's one of those settings that hides in plain sight. 🔧

RockyMaker | Posts: 847

@Kingy classic Victron gotcha with lithium. Worth checking your absorption time settings in VictronConnect — the default "adaptive" absorption is designed around lead-acid behaviour and can cut short embarrassingly quickly when it sees the voltage climb fast (as lithium does).

Try switching to fixed absorption time and setting something sensible like 20-30 minutes. Also double-check your tail current setting — if it's set too high relative to your bank capacity, it'll trigger the float transition prematurely.

What firmware version are you running? There were some known quirks a couple of versions back that affected this specifically with third-party BMS setups. If your Fogstar BMS is controlling charge via a VE.Bus or just voltage-only, that'll change the diagnosis completely.

VanKen | Posts: 214

Mine did the same in the static — turned out the tail current setting was doing all the heavy lifting and declaring "job done" the moment it saw a slight dip, like a contractor knocking off at 2pm and calling it a full day. 🔧

Worth diving into VictronConnect and bumping that tail current threshold down — it's usually set way too generously out of the box for lithium. Also double-check your battery capacity figure is actually correct in the settings, because if Victron thinks you've got a smaller bank than you do, it'll hit its targets embarrassingly early like a sprinter who misread the finish line.

PennineNomad | Posts: 1,203

Had the identical issue on my narrowboat — the root cause for me was that the absorption voltage was set just slightly too close to the resting voltage of the Fogstar cells, so the Multiplus thought it had hit target and bailed out early.

Worth checking in VEConfigure:

• Absorption voltage — push it up to what your BMS actually wants (typically 3.45–3.65V per cell)
• Repeated absorption time — make sure it's not set to zero
• Also cross-reference what your BMS is actually reporting via VE.Bus; sometimes the Multiplus is doing exactly what it's told, the profile is just wrong for lithium

@VanKen is right about tail current too, but I'd sort the voltage settings first — tail current won't save you if the absorption threshold is fundamentally miscalibrated.

BreezySparky | Posts: 412

Worth adding — if you're using a Victron BMV or SmartShunt alongside the Multiplus, make sure the two are actually talking to each other via VE.Smart networking. Without that, the Multiplus is flying blind on state of charge and will just guess based on voltage alone.

Had this exact thing catch me out with my garden office setup. Fogstar 280Ah cells sitting at 85% according to the BMV, but the Multiplus had already declared float because terminal voltage crept up quickly under light load. Once I enabled the network and let the BMV feed SoC data directly to the charger, it behaved itself properly.

Also double-check your battery capacity figure in VEConfigure — if it's set too low, the tail current threshold gets hit way earlier than it should.

BayTim | Posts: 89

Same issue on my boat last year, drove me absolutely mad before I figured it out. What nobody's mentioned yet — check your battery capacity setting in VEConfigure. If it's set too low, the Multiplus underestimates how much charge is actually needed and bails out early. Mine was set to the default rather than my actual Fogstar pack size.

Also worth checking whether your DC cable run has enough voltage drop that the charger thinks absorption voltage has been reached at the terminals when it genuinely hasn't at the battery.

@BreezySparky is hinting at something important too — the SmartShunt integration via VE.Smart networking made a noticeable difference on mine once I actually configured it properly rather than just plugging it in and assuming it worked. Don't make my mistake there.