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

Had this exact issue last summer with my 100/30. Turned out to be a combination of things worth checking:

Absorption time — mine was set to "adaptive" which calculates time based on the previous night's discharge. If the battery didn't discharge much, it shortens absorption. Sounds clever but it caused all sorts of confusion with my Fogstar Drift LiFePO4 cells.

Tail current — this one caught me out. If the charge current drops below the tail current threshold before absorption time is up, it jumps to float early. Worth checking what yours is set to in VictronConnect. I had mine way too high.

Battery temp sensor — if it's reading incorrectly it'll mess with the voltage targets and make the controller think absorption is done when it isn't.

My fix was switching from adaptive to fixed absorption time (I use 2 hours) and dropping the tail current to around 1-2% of battery capacity. Been solid ever since.

Also — what battery chemistry are you running? The defaults in VictronConnect aren't always great for lithium, and a lot of people just leave them as-is after install.

Anyone else found adaptive mode more trouble than it's worth on smaller setups? I'm genuinely not convinced it adds much for a cabin system that has pretty predictable usage patterns. Would be curious whether others have just gone fixed and forgotten about it.

Hey @EmmaEdwards82, good shout on the absorption settings. One thing I'd add that catches people out — check your battery temperature. If you've got a BMS or temp sensor reporting even slightly elevated temps, the Victron will deliberately curtail absorption and drop to float early as a protective measure. Completely normal behaviour but blooming frustrating when you don't realise that's what's happening.

Also worth checking in VictronConnect whether your tail current threshold is set sensibly. If it's too high (say 4-5% of battery capacity), the controller thinks the battery's full before it actually is and bails out early. Dropping it to around 1-2% made a noticeable difference on my setup. Have a dig through the history tab too — it'll show you exactly what triggered the transition each time. 👍

Good point on absorption, but the one that had me stumped for a week on my garden office setup was the temperature compensation — if you've got a Victron SmartShunt or BMV in the loop sending temp data, and your sensor's reading wonky, the MPPT will happily cut absorption short thinking the battery's warmer than it is. Fogstar Drift cells especially seem fussy about this. Chuck the VictronConnect app open and check the "charged voltage" figure in the battery monitor history — if it's consistently lower than your set absorption voltage, something upstream is telling it to back off early.

Something that hasn't been mentioned yet — wire gauge and connection resistance. Had this on my shepherd's hut setup last year, Victron 100/20 kept thinking batteries were full ages before they were.

The MPPT reads voltage at its own terminals, so if you've got dodgy crimps or undersized cable runs, there's a voltage drop happening and the controller thinks the battery is higher than it actually is. Mine had a knackered Anderson connector I'd bodged on — looked fine visually but was adding maybe 0.3-0.4V under load.

Worth doing a proper voltage check directly at the battery terminals vs what the controller's reporting. If there's a meaningful difference that's probably your culprit. Victron's battery sense cable or the wireless dongle sorts it properly but fixing the actual wiring is obviously the right answer first.

Great points all round. One thing worth adding that I haven't seen mentioned yet — check your battery voltage sense settings. If your MPPT is only using internal voltage sensing (measuring at the controller terminals rather than directly at the battery), voltage drop across your cables can fool it into thinking the battery is fuller than it actually is. The controller "sees" a higher voltage and kicks into float prematurely.

If your Victron supports remote voltage sensing (the smaller sense terminals on some models, or via a VE.Smart network with a BMV monitor), enabling that makes a genuine difference. Sorted exactly this problem on my narrowboat setup last year — absorption time went from cutting out embarrassingly early to actually completing a proper charge cycle. Well worth five minutes investigating before you start changing absorption thresholds manually.