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

Had this exact drama on my narrowboat last summer — Victron SmartSolar 100/30 deciding it was "done" by about 11am like it was on a half day.

Turned out my battery voltage sense was the culprit. The MPPT was reading voltage at the controller terminals rather than at the battery itself, so with even a bit of cable resistance it thought the Fogstar lithiums were fully cooked when they absolutely weren't. Enabling the VE.Smart networking so it pulls voltage direct from the BMV-712 shunt sorted it overnight — absorption time jumped from 45 minutes to a proper 3+ hours.

Few other things worth checking:

• Absorption voltage set too low — lithium profiles especially are fussy, even 0.1V out can trigger early float
• Tail current settings — if you're running a BMS that smooths current draw, the MPPT can mistake low tail current for full charge
• Temperature compensation — on a cold hull it'll adjust voltage down and bail early

Also worth checking you're not accidentally running a lithium preset when your bank is AGM or vice versa, because I've seen folk do exactly that and spend three weeks baffled.

What controller firmware are you on? Victron pushed an update a while back that tweaked the absorption end algorithm — worth making sure you're current via VictronConnect.

Anyone else found the VE.Smart networking was the magic fix here, or was yours something different? Curious whether this is more common on boats where cable runs are longer.

@MariaJones classic Victron gotcha that one — I fell into the same trap with my tiny house build.

Mine was slightly different though. The absorption time was set far too short in the defaults. Victron ships these units assuming a relatively small battery bank, so if you've upgraded to a decent-sized LiFePO4 pack — I'm running Fogstar Drift cells — the controller gives up before the bank is anywhere near full.

Worth checking your tail current setting too. If that's configured as a percentage of a small nominal capacity, it'll trigger float prematurely on a larger bank.

The fix for me was:

• Bumping absorption time to something sensible
• Setting tail current as a fixed amperage rather than percentage
• Enabling the battery temperature sensor

VictronConnect makes all of this fairly painless once you know where to look.

Same issue hit me on the boat last season — but in my case it was the absorption time set way too short rather than voltage sense.

Worth checking your absorption time settings in VictronConnect. If it's on the fixed-duration mode and set to something like 1hr, a partly-charged bank will get booted to float before it's properly topped up.

I switched mine to the adaptive absorption algorithm and it made a noticeable difference — the controller now actually responds to what the batteries need rather than just watching the clock.

Also worth double-checking your battery capacity figure is entered correctly if you're using that to calculate absorption time. Had mine set for 100Ah when I'd upgraded to 200Ah Fogstar cells and never updated it. Daft mistake but easy to miss.

Great thread, this comes up a lot! One thing nobody's mentioned yet — worth checking your absorption voltage threshold itself. If it's set even slightly low for your battery chemistry, the controller reaches it too quickly and thinks the job's done before the batteries are anywhere near full.

Also @MariaJones and @RKE_Builds, if you're on a boat with long cable runs, voltage drop between the controller and batteries can cause all sorts of confusion here. Even with proper sense wiring, I'd recommend double-checking your cable sizing calculations — I've seen people lose 0.3-0.4V across undersized cabling which completely throws the charging profile off.

The VictronConnect app is your friend for diagnosing this — pull up the history graphs and you can see exactly when it transitioned and at what voltage. Makes fault-finding much quicker.

Great thread for anyone troubleshooting this — really common source of confusion.

One thing worth adding beyond what @MariaJones, @RKE_Builds and @KeithMartin have covered: check your tail current setting in VictronConnect. This is the threshold at which the MPPT decides absorption is "complete" and drops to float.

On my static caravan setup with Fogstar Drift LiFePO4 cells, I found the default tail current (set as a percentage of battery capacity) was far too aggressive — the controller was interpreting a modest drop in charge acceptance as "battery full" when it absolutely wasn't.

Worth cross-referencing your battery manufacturer's spec sheet for the recommended tail current cutoff — LiFePO4 vs AGM behave quite differently here.

Also, if you're new to Victron kit generally, don't be put off by the learning curve — the VictronConnect app makes most of this genuinely straightforward once you know what you're looking for.

Spent three weeks convinced my Victron Connect app was lying to me before realising my battery temperature was throwing the whole compensation curve off — if you've got a BMV or a Smart Battery Sense fitted, double-check the temperature coefficient setting isn't quietly sabotaging your absorption phase every warm day. 🌡️