Victron MPPT keeping my batteries at 80% even with float set to 14.4v — anyone else had this?

Had almost the exact same head-scratcher on my narrowboat last summer. Spent a good few evenings staring at the VictronConnect graphs wondering why my Fogstar 100Ah lithiums were sitting stubbornly at 80% despite the float voltage looking perfectly sensible on paper.

Turned out the culprit was the absorption time being cut short. The MPPT was hitting the absorption voltage threshold, deciding the battery was "close enough," and dropping to float before the cells had actually topped off properly. Classic tail current behaviour — Victron's adaptive algorithm is clever but it can get too conservative, especially if your bank has seen a few heavy cycles.

A few things worth checking:

• BMS comms — if you're running a Cerbo GX or similar, check whether the BMS is sending charge current limits that are throttling things prematurely
• Temperature compensation — colder ambient temps can skew the voltage readings and make the controller think it's done when it isn't
• Absorption time minimum — bump it up manually in the Charger settings and see if that shifts things

The other possibility, and this caught me out, is that your battery's actual state of charge calculation is drifting. What are you using to monitor SoC — a SmartShunt? If it's not been properly zeroed recently it can report 80% when you're genuinely at 95%+.

Worth pulling up the VRM history graphs if you've got portal access — the absorption/float transition timestamps tell a proper story.

What battery chemistry are you running? Makes a difference to where to look first.

@FZ_Builds classic Victron gotcha that one! Check your absorption time settings — if you've got it on adaptive absorption, the controller learns from previous cycles and can cut absorption short if it thinks the battery is "full enough." Lithiums don't behave like AGM so it gets confused.

Also worth checking: is your battery voltage sense coming from the controller terminals or do you have a separate sense wire? Voltage drop across your cabling could mean the controller thinks it's hitting 14.4v at the terminals whilst the actual battery is sitting lower.

Pull up the history tab in VictronConnect and check your absorption time column — if it's showing 0h or very short durations, that's your culprit. Had exactly this on my tiny house build until I switched to fixed absorption time rather than adaptive.

Worth checking whether you've got BatteryLife enabled in VictronConnect — it's on by default and deliberately caps charge to around 80% to preserve cycle life. Easy to miss since it's buried in the algorithm settings rather than the voltage config.

Turned mine off on the van build once I'd set proper charge parameters for the Fogstar cells. Made an immediate difference.

Also double-check your battery voltage sense — if the MPPT is reading voltage at the controller terminals rather than the battery terminals, voltage drop across the cable can fool it into thinking absorption is done early. Worth enabling remote voltage sensing if your setup allows it.

@WonkyMechanic beat me to BatteryLife but there's another one nobody's mentioned — check your State of Charge tail current setting. If the MPPT thinks absorption is "done" before the battery's actually full (because the tail current threshold is set too high), it'll drop to float prematurely and you'll sit at ~80% indefinitely.

On my boat setup I had this exact issue. VictronConnect was showing float voltage correctly at 14.4v but actual SoC was nowhere near 100%. Turned out my tail current was set to something daft like 4A on a 100Ah bank.

Also — and this is pedantic but it matters — are you certain your voltage measurement point is at the battery terminals rather than the controller? Cable voltage drop can make 14.4v at the MPPT look like considerably less at the cells.

@CliffGazer raises a good point on tail current, but one more thing worth checking: your absorption voltage and float voltage are two separate stages, and if your battery isn't reaching the tail current threshold during absorption, it'll time out and drop straight to float — which on Fogstar cells typically settles around 13.4v, nowhere near the 14.4v you're expecting.

Pull up the History tab in VictronConnect and check your actual absorption duration. If it's consistently hitting the maximum time rather than terminating early via tail current, your system is undersized for the load or the absorption voltage itself is set marginally too low for your cell chemistry.

I had similar behaviour on my garden office setup — turned out my absorption was 14.2v when Fogstar's spec wants 14.4v minimum. Two tenths of a volt made a noticeable difference.

@CarlBaker all valid, but don't overlook the wiring losses either — if your cable run to the battery is marginal, the MPPT sees 14.4v at its terminals while the actual battery voltage is quietly laughing at you from 13.8v.