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

Had this exact issue with my static earlier in the year. The MultiPlus was dropping into float at around 80% according to my BMV-712, which obviously isn't ideal when you're trying to top up after a run of cloudy days.

Turned out my battery capacity settings in VE.Configure were slightly off — I'd entered the original rated capacity rather than the actual usable capacity of my Fogstar Drift cells. Once I corrected that and also adjusted the charged voltage and tail current parameters, it started behaving much more sensibly.

A few things worth checking:

• Tail current setting — this is probably the main culprit. If it's set too high (as a percentage of capacity), the unit thinks the battery is full before it actually is
• Absorption voltage — is it set correctly for your battery chemistry? LiFePO4 vs AGM makes a big difference here
• Battery capacity entered in the MPPT/BMV — does it match what's in the MultiPlus settings?

Worth downloading VictronConnect or VE.Configure and having a proper look at the charge algorithm parameters if you haven't already. Victron's defaults are fairly conservative and don't always suit every battery setup.

What batteries are you running? That might help narrow it down — lithium setups in particular can be fussy about these thresholds. Also, are you using a Cerbo GX or similar? Having everything networked together via VE.Bus made a noticeable difference to how consistently mine charges now.

Would be interested to know if anyone else has found other causes — I feel like this comes up more often than it should.

Had this exact same saga with my motorhome setup last autumn. Turned out my battery capacity settings in VictronConnect were way off — I'd never properly configured the charged voltage and tail current parameters for my Fogstar Drift lithium bank.

The MultiPlus was seeing what looked like a full charge based on wrong reference points.

Worth checking two things in VEConfigure:

• Absorption voltage — is it actually matched to your battery spec?
• Tail current — the default is often far too high for lithium, so it triggers float prematurely

Once I dropped the tail current to around 1-2% of capacity, the BMV-712 and MultiPlus finally agreed with each other and started hitting genuine full charges.

@YorkshireCamper what battery chemistry are you running? Makes a big difference to where these thresholds should sit.

The BMV-712 and MultiPlus need to be talking to each other properly via VE.Smart networking, otherwise the MultiPlus is making absorption/float decisions based solely on its own voltage sensing rather than the BMV's state-of-charge data. Worth checking in VictronConnect whether your Smart Networking is actually active and both devices appear in the same network.

Also, have a look at your tail current setting — this is what actually triggers the float transition. If it's set too high (default is often 2A, which is fine for small banks but will fire too early on anything substantial), the MultiPlus sees that current figure and assumes the battery is full long before it really is.

On my narrowboat I run a 400Ah Fogstar Drift LiFePO4 bank and had to drop tail current to 0.5% of capacity before float timing became sensible.

Classic Victron "I've decided we're done here" energy 😄

Had almost this exact drama on Perseverance (my narrowboat, not the Mars rover — though sometimes it feels like I'm troubleshooting from another planet).

The culprit for me was the Peukert exponent set wrong for my Fogstar

Had almost this exact same issue on my setup last winter. Worth checking your charged voltage and tail current settings in VE.Configure — mine were way off from factory defaults for my battery bank size. The tail current especially; if it's set too high the MultiPlus thinks absorption is complete when it really isn't.

Also double-check your battery capacity figure is accurate in both the BMV and the MultiPlus separately — @FenlandSolar makes a good point about VE.Smart networking but even with that sorted, mismatched capacity figures caused me no end of grief.

What battery chemistry are you running? Lithium vs AGM vs flooded lead acid can make a massive difference to what settings you actually need. Victron's defaults don't always suit real-world installations out of the box.

@Wez1993 nailed the tail current point, but also worth checking if your battery temp sensor is lying to you — mine on Perseverance was reading the bilge temperature instead of the actual cells, so the Victron thought the batteries were warmer than they were and bailed out of absorption early like it had somewhere better to be.