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

Had exactly this on my boat last summer. Victron SmartSolar 100/30, brand new Fogstar 200Ah lithium, and it was jumping to float after maybe an hour of absorption — battery nowhere near properly topped up.

Turned out my absorption voltage was set slightly too low for the battery's actual specs. Bumped it from 14.2V to 14.4V and the tail current threshold was also the culprit — it was cutting absorption short because the current had dropped to what looked like a full charge, but the battery was only sitting around 85-90% SOC.

A few things worth checking:

• Tail current setting — if it's too high, MPPT thinks the battery is full when it isn't. Drop it to around 2-4% of battery capacity
• Absorption time — you can set a minimum absorption time in VictronConnect to stop it cutting off early
• Battery temperature — colder temps can affect how the battery accepts charge and confuse the controller

Also worth checking whether you're using the built-in Li preset or a custom profile. The presets are fine as a starting point but they're quite conservative.

What battery chemistry are you running? Makes a big difference to how you configure this. And are you using a BMV or SmartShunt alongside it? Getting accurate SOC readings from a dedicated monitor rather than relying on the MPPT's estimate alone changed everything for me.

Would be good to know what your current settings look like — screenshot from VictronConnect would help diagnose it faster.

@TracyMitchell oh this sent me DOWN a rabbit hole last autumn with my shepherd's hut setup — almost identical scenario, Victron MPPT, Fogstar lithium, same premature float behaviour.

Turned out my battery voltage sense was reading at the controller terminals rather than the battery itself. Even tiny cable resistance was convincing the MPPT the battery was fuller than it actually was.

Two things worth checking:

• Enable remote battery sensing in VictronConnect if your BMS supports it (or run a dedicated sense wire)
• Check your tail current setting — on lithium it should typically be around 1-2% of capacity, so ~2-4A on a 200Ah pack

Mine was still on the AGM default profile which had completely wrong absorption termination logic for lithium chemistry. Switched to a proper lithium preset and it cracked on properly from then on.

@TracyMitchell classic one this — check your absorption voltage threshold in the MPPT settings. Victron defaults are set for AGM/lead, so on lithium the tail current cutoff matters more than time.

In VictronConnect, set a proper tail current (usually 2-4% of battery capacity — so ~4-8A on a 200Ah pack). Once current drops below that threshold it'll correctly end absorption rather than timing out early or cutting short randomly.

Also worth checking your battery's actual charge parameters with Fogstar directly — their 200Ah has specific recommended voltages that don't always match Victron's lithium presets out of the box.

Had the same faff on my boat before I sorted the tail current setting. Night and day difference after.

@TracyMitchell had the same head-scratcher with my Fogstar 100Ah last spring! One thing worth checking that nobody's mentioned yet — the tail current setting in VictronConnect. By default it's often set quite high (around 4% of battery capacity), so the MPPT sees current dropping as the battery approaches full and decides it's done. Lithium cells can accept charge very efficiently towards the end, so it hits that tail current threshold faster than you'd expect. Try dropping it to around 1-2% and see if absorption holds longer. Also worth double-checking your battery capacity is correctly entered in the app — if it thinks you've got a smaller bank, the maths goes wonky. @VivaroNomad's rabbit hole sounds familiar! The VictronConnect app makes all this fairly accessible once you know where to look.

Is your BMS talking to your MPPT?

Got bitten by exactly this in my motorhome last year — sat there scratching my head for weeks.

Turned out my Fogstar's BMS was sending a charge complete signal via the VE.Smart network and the Victron was just... believing it. Like a golden retriever

Really good thread this. One thing I'd add that hasn't been touched on yet — have you checked your battery temperature? Lithium BMSs can report a high cell temp to the MPPT (if you've got comms set up) and the controller will deliberately curtail absorption as a protective measure. Even sitting in a warm engine bay or getting direct sun on the battery casing can trigger it.

Also worth looking at your tail current setting in VictronConnect. If it's set too high, the MPPT interprets the dropping charge current as "battery full" and exits absorption prematurely. Fogstar cells are quite efficient and can genuinely pull less current than you'd expect toward the end — so the controller thinks it's done when it isn't quite there yet.

Drop your tail current to around 2-4% of battery capacity and see if that makes a difference. Worked for me on a similar setup.