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

Had exactly this on my garden office setup last summer. Victron SmartSolar 100/30, brand new Fogstar 200Ah LiFePO4, and the controller was declaring victory and dropping to float by mid-morning on a decent day. Battery was sitting at maybe 60% actual capacity according to the BMV-712.

Turned out to be a combination of two things:

Tail current was set too high. The default assumes a much larger or older battery bank. Drop it down — I went to around 1% of battery capacity and it made a significant difference.

Absorption time was too short. Worth checking whether you've got it on the adaptive setting, because on smaller banks it can make some odd decisions early in the season when the solar history isn't established yet.

Fixed mine by switching to a custom LiFePO4 profile rather than the preset. Set absorption at 14.2V, float at 13.5V, and dialled the tail current right down. The battery now consistently hits 95-98% before dropping off.

One thing worth checking — are you monitoring actual state of charge through a shunt-based monitor, or just going off the MPPT's estimates? The SmartSolar can be a bit optimistic without proper current sensing in the loop.

What's your battery chemistry and bank size? Makes a big difference to where the problem likely sits.

Had the exact same headache with my cabin setup. Turned out my absorption voltage was set too low — LiFePO4 needs it bang on 14.2-14.6V and the absorption time long enough to actually complete.

Also worth checking your battery capacity setting in VictronConnect. If it thinks you've got a smaller bank than you do, it'll calculate absorption time as finished way too early.

@FormerMariner36 — are you using the Lithium preset or a custom profile? The built-in Lithium preset on mine was rubbish out of the box. I ended up following Fogstar's own recommended charge settings and dialling them in manually. Made a massive difference.

Also check your tail current setting — that's often the culprit for premature float.

@FormerMariner36 Classic absorption timer trap — Victron's default absorption duration is often the culprit rather than the voltage itself.

On my motorhome rig I learned this the hard way. The SmartSolar calculates absorption time based on lead-acid assumptions, so a partially discharged LiFePO4 can fool it into thinking it's full because the voltage rises so quickly (flat discharge curve, then sudden spike near the top).

Check your BatteryLife settings and, crucially, set a minimum absorption time — I'd suggest at least 30 minutes for a 200Ah pack. Also worth enabling the tail current setting if your firmware supports it; that way float only triggers once charge current actually drops below a set threshold rather than purely on time.

@GlenWard makes a fair point on voltage, but I'd wager the timer is the real villain here.

@LiFePO4Nerd raises a fair point but nobody's mentioned the tail current setting yet — that's the real magic for LiFePO4, set it to ~2% of capacity (4A on a 200Ah bank) and the Victron will only exit absorption when the battery actually stops accepting charge rather than just timing out like an impatient postman.

@FormerCop nailed it on tail current — had mine set to the Victron default and my Fogstar was clocking off at about 70% like it had done a full shift, dropped it to 2% of capacity and suddenly it actually bothers to finish the job properly before sulking off to float.

@FormerCop and @BorderVanLifer are absolutely right on tail current — but worth adding that the percentage matters relative to your battery capacity.

On my motorhome setup (2x Fogstar Drift 200Ah in parallel), I run tail current at 4% of capacity — so roughly 16A before float kicks in. Victron's default 1A is laughably low for larger banks and will trigger float prematurely almost every time.

In VictronConnect, go to:
Expert Mode → Tail current → set as % of rated capacity

Also double-check your absorption voltage is actually matching Fogstar's spec sheet — they recommend 3.55V/cell (14.2V for 12V) rather than the 14.4V Victron often defaults to. Running too high can paradoxically look like early float because the BMS throttles charge current before the bank is genuinely full.

Both settings together made a massive difference on my van.