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

Had this exact issue last summer with my 100/30. Turned out my absorption voltage was set a touch low and it was hitting the threshold quicker than it should — bumped it up by 0.2V and the problem largely sorted itself.

Worth checking a few things:

• Battery type setting — if it's on the wrong profile it'll use the wrong absorption/float thresholds entirely
• Absorption time — check if you've got it on adaptive or fixed. Adaptive can be very aggressive on a sunny day when the battery is already reasonably full
• Tail current setting — this is the one most people miss. If tail current is set too high, it thinks absorption is "done" and drops to float early

What battery are you running? Lithium or lead? Makes a big difference to how you'd approach this. I've got Fogstar Drift 200Ah on mine now and had to dial things in properly via VictronConnect before it behaved sensibly.

Also — are you monitoring via the app or do you have a Cerbo/Venus device? The history graphs in VictronConnect are actually decent for spotting patterns. Can see exactly when it's transitioning and correlate it with irradiance.

Wouldn't panic too much if the battery is genuinely getting full — MPPT doing its job in that case. But if it's dropping to float at 60-70% and staying there, that's a problem worth chasing down.

What does your absorption voltage look like currently? Post your settings and someone here will probably spot the issue pretty quickly.

@Wez1961 worth also checking your tail current setting — this is the one that catches people out more than absorption voltage IMO. If tail current is set too high (say 4–5% of battery capacity), the controller thinks the battery is full long before it actually is.

On my narrowboat setup with Fogstar Drift LiFePO4 cells, I had mine set at the Victron default which was wildly optimistic for my actual bank size. Dropped it to around 1–2% and absorption time extended dramatically — batteries are noticeably better topped up now.

You can adjust this in VictronConnect under the charger settings, assuming you've got the Bluetooth dongle or a Smart unit. It's buried a bit but it's there.

Great shout from @PanelEwan on the tail current — that's exactly what caught me out on my 75/15 last year. Mine was left on the default 2A which was far too high for my battery bank size. As a rough guide, tail current should typically be around 1-2% of your battery's total amp-hour capacity, so if you're running a 200Ah bank you'd want it somewhere around 2-4A maximum, possibly lower. Drop it too high and the controller thinks the battery's full well before it actually is. Worth having a proper look in the VictronConnect app under the battery settings — it's all adjustable in there and takes about two minutes once you've got it open. What size bank are you running @Wez1961?

Both @PanelEwan and @Wez1961 have covered the main culprits, so I'll add one that gets overlooked — battery temperature. If you're running without a temp sensor (or the sensor's poorly placed), the MPPT will use a fixed compensation value. On a warm day the controller thinks the battery needs less voltage than it actually does, so it hits float early.

Worth checking in the VictronConnect app under battery settings → temperature compensation. If you're on a boat or van like me, ambient swings are massive and this matters more than most people realise.

Also double-check your battery capacity setting if you're on a Smart MPPT — undersizing it relative to your actual bank makes the tail current trigger prematurely because it calculates percentage-based thresholds off that figure.

Good points all round from @Wez1961, @PanelEwan and @RayWatson81 — covering most of the usual suspects there.

One thing I'd add from my own setup (lithium on a narrowboat): make sure you're using a battery preset that actually matches your chemistry. Victron's defaults are designed for flooded lead-acid and can behave oddly with LiFePO4 if you haven't gone in and built a custom profile. I was scratching my head for weeks before I realised I'd never changed the preset after swapping from AGM to Fogstar Drift cells.

Also worth connecting via VictronConnect and watching the live data during a charge cycle rather than just checking after the fact — you can actually see the moment it drops to float and work backwards from there.