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

Had this exact issue a few months back with my 100/30. Battery would show maybe 70% on the Victron app but the MPPT had already switched to float. Drove me absolutely mad trying to work out what was going wrong.

Turned out my battery voltage sensing was the culprit — I hadn't run a dedicated sense wire to the battery terminals, so the controller was reading a slightly inflated voltage due to resistance in the cable run. Small difference, but enough to fool it into thinking absorption was done ahead of schedule.

Few things worth checking:

• Battery temperature compensation — if you're using a "warmer" install location, the controller might be adjusting the absorption target downward
• Absorption time settings — is yours set to adaptive or fixed? Adaptive can be very short if the battery appeared "full" at the start of the day
• State of charge vs voltage — are you running a Victron BMV or SmartShunt alongside it? The MPPT on its own is just going by voltage

What batteries are you running? Lithium (particularly Fogstar or similar) sometimes needs the absorption voltage and time tweaking quite specifically compared to what Victron's defaults assume.

Also worth enabling the VE.Smart Networking if you've got a BMV — letting the MPPT take its cues from actual measured SoC rather than just terminal voltage made a noticeable difference on my setup.

Curious whether others have found the adaptive absorption particularly aggressive in summer when panels are producing well from the off?

@PVKing classic symptom of incorrect battery voltage thresholds — check your absorption voltage is set high enough for your battery chemistry. With AGM it should be around 14.4V, LiFePO4 needs 14.2–14.6V depending on the cells.

More likely culprit though: the tail current setting. If it's set too high, the MPPT thinks the battery is full when it isn't. On my 100/50 running Fogstar Drift 200Ah, I dropped tail current to 1% of capacity and it sorted it immediately.

Also worth checking:

• Battery temperature sensor fitted? Compensation can skew readings
• Any voltage drop between controller and battery terminals?

Worth running VictronConnect and checking the history tab — you can see exactly when it switched and what voltage it was at. That'll tell you a lot.

@PVKing had almost identical on my narrowboat with a 75/15. Worth checking your tail current setting in VictronConnect — if it's set too high, the MPPT thinks the battery's full way before it actually is.

Mine was defaulting to something daft like 2A on a 100Ah Fogstar lithium. Dropped it to around 1% of battery capacity and it sorted itself out overnight.

Also double-check your battery capacity is entered correctly in the app — if Victron thinks you've got a smaller bank than you do, the tail current trigger fires too early.

@PVKing nine times out of ten it's the absorption time being set too short rather than the voltage — mine on my van build was defaulting to a laughably brief period that would've left my Fogstar lithiums about as charged as a politician's promises.

Check ESS → Charger → Absorption Time in VictronConnect and bump it up; also worth double-checking your battery capacity is entered correctly, because Victron uses that figure to calculate when it reckons the job's done.

@AnneButler and @PanelBuff have covered the main culprits already so I'll add something slightly different — check whether you've got adaptive absorption enabled. On my boat setup the MPPT was using the previous day's charging data to shorten absorption time, which sounds clever but caused real headaches when I had a couple of overcast days in a row. The algorithm gets confused and starts cutting absorption embarrassingly short.

Go into VictronConnect → your charger → settings and have a look at whether it's on fixed or adaptive. Switching to fixed absorption time sorted mine immediately. Also worth double-checking your battery type is set correctly — had mine on AGM defaults when it should've been set to LiFePO4, which threw everything off.