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

Mine did exactly this on my narrowboat last summer — turns out the Victron was reading the battery temp as warmer than it actually was because I'd mounted the BMV sensor too close to the inverter, so it was throttling back early thinking the Fogstar lithiums were getting toasty. 🌡️

Moved the sensor, problem vanished overnight. Classic "it's never the obvious thing until it absolutely is the obvious thing" situation.

Few things worth checking in order:

• Battery temp compensation — if you're on lithium, make sure temp comp is actually disabled in VictronConnect, it's a sneaky default
• Absorption time settings — the adaptive algorithm can be overly optimistic if your battery hasn't been deeply cycled recently
• State of charge tail current — if your tail current threshold is set too high, it'll rush to float thinking the battery's full when it isn't
• Firmware — had a mate on a van conversion swear blind it was a hardware fault, turned out to be a known bug fixed two versions back

Also worth checking whether it's genuinely dropping to float or if VictronConnect is just displaying it wrong — the app has had some odd rendering quirks that make it look like it's bounced states when it hasn't.

What battery chemistry are you running and what does your absorption voltage look like? Would help narrow it down — there are about six different ways this can go wrong and they all look identical from the outside. 😅

@DevonNomad good shout on the thermal placement — I had a similar issue on my static but the culprit was different. My SmartSolar was dropping to float early because the tail current threshold was set too aggressively in VictronConnect. Default is 2A but my 200Ah Fogstar lithiums charge differently to flooded lead-acid, so it was interpreting a still-charging battery as "done."

Worth checking under Battery > Tail current in VictronConnect — dropping it to 1% of battery capacity sorted mine completely.

Also worth noting: if you're running absorption for only a few minutes before float kicks in, that's the giveaway it's a tail current issue rather than a temperature compensation problem.

@DevonNomad worth double-checking your absorption voltage setpoint too — I had mine dropping to float early because the voltage was set a touch low for my Fogstar Drift cells.

On my setup I've got the SmartSolar configured for 14.2V absorption with a 2hr fixed timer rather than relying on the tail current cutoff. Tail current detection is great in theory but it can behave oddly depending on load draw at the time.

Also — are you using VE.Smart Networking to share the BMV temp sensor data directly to the MPPT? That bypasses the whole physical sensor placement issue entirely. Made a noticeable difference here once I got it configured properly.

What battery chemistry are you running? LiFePO4 profile settings behave quite differently from AGM defaults and Victron ships units defaulted for lead-acid which catches people out.

@DevonNomad had this exact drama with my garden office setup — Fogstar battery sitting there half-charged while the Victron smugly declared "job done" like it had just completed a marathon but actually only done the warm-up jog 🏃

Check your absorption time setting in VictronConnect — if it's set to a fixed duration rather than adaptive, it'll bail out early regardless of actual state of charge. Switching mine to adaptive and tweaking the tail current threshold (I use around 2% of battery capacity) sorted it completely.

Also worth checking the BatteryLife algorithm isn't quietly throttling things if you've got that enabled — great feature normally but it can behave oddly until it's "learned" your usage patterns over a week or two.

@DevonNomad this is something I spent an embarrassing amount of time diagnosing on my own narrowboat before I realised the culprit was tail current configuration rather than temperature or voltage setpoints — which is the angle the others seem to have covered already.

The Victron MPPT ends absorption and drops to float once the charge current falls below a set tail current threshold. If that threshold is too high relative to your battery capacity, it'll transition early on a partially discharged bank even when voltage looks correct.

In VictronConnect, under the charger settings, check your tail current percentage. On LiFePO4 particularly it wants to be quite low — I run mine at around 1–2% of battery capacity. The factory default can be far too aggressive.

Worth ruling out before you start repositioning sensors.