Anyone else had grief with a Victron SmartSolar 100/30 dropping to float way too early?

I've got a 200Ah lithium (LiFePO4) bank paired with a Victron SmartSolar MPPT 100/30 and two 175W panels wired in series. Running the system in my narrowboat and generally it's been solid, but lately I've noticed the controller is jumping to float after only about 30–40 minutes of absorption, even when the batteries were sitting at around 50% SOC the night before. I'd have expected a good couple of hours of absorption at minimum.

I've got the battery profile set to lithium preset in the VictorConnect app — absorption at 14.2V, float at 13.5V, no tail current set because the preset doesn't expose that easily. I'm wondering if the issue is that it's hitting the absorption voltage target quickly on a sunny morning and then just... giving up. The batteries seem fine and are reading 98–99% on the BMV-712, but I'm a bit suspicious whether that SOC figure is genuinely accurate or whether the MPPT is cutting absorption short and the BMV is just following along.

Has anyone dug into the tail current settings via the expert mode in VictorConnect, or used a custom profile to stretch absorption out a bit? I'm also curious whether this is actually a problem at all with LiFePO4 — I know they behave differently to AGM — or if I'm just overthinking it because the numbers look odd compared to what I was used to with lead acid.

@KMV_Marine looks like your post got cut off, but I'll hazard a guess you're seeing the controller jump to float before the battery's properly full — classic symptom.

Nine times out of ten on LiFePO4 this is a tail current issue. Victron's default absorption exit condition is time-based, but if you've got "tail current" enabled in VictronConnect, it'll drop to float the moment charge current falls below that threshold — which on a healthy lithium bank can happen surprisingly early.

Check these in VictronConnect:

• Absorption voltage — should be ~14.2V for most LiFePO4
• Float voltage — set to 13.5V or lower, some people just match absorption
• Tail current — either disable it or set it low (1-2% of capacity)

I had identical behaviour on my static caravan setup with a Fogstar 200Ah until I sorted the tail current setting. What BMS are you running?

@KMV_Marine your post did get cut off, but I'll add something @KentBoater likely hasn't covered yet — check your tail current setting in VictronConnect. On LiFePO4 this is the key parameter that tells the MPPT "absorption is done."

Default is often set for lead-acid at around 2A or a percentage that suits flooded cells, not lithium.

For a 200Ah LiFePO4 bank you'd typically want tail current somewhere around 2–4% of capacity (so 4–8A). If it's set too high, the controller thinks the battery is full and drops to float prematurely — even if it isn't.

Also worth double-checking your absorption voltage is actually set correctly for LiFePO4 (14.2–14.6V depending on your BMS specs). Had almost this exact scenario on my shepherd's hut setup before I dug into the VictronConnect presets properly.

@KMV_Marine your post got cut off AND @NaeClue13's reply got cut off. Are you both on the same dodgy internet connection? 😂

Genuine question though — are you using the VictronConnect app to monitor what's actually happening during the charge cycle? Because I spent three weeks convinced my SmartSolar 75/

@PeakCamper the irony is killing me.

@KMV_Marine assuming you're seeing early float transitions — the usual culprit on LiFePO4 with a SmartSolar 100/30 is the absorption time being set too short, or your tail current threshold being too aggressive. In VictronConnect, check your expert mode settings. On lithium profiles the default tail current (2-3% of capacity) can trip float prematurely if your panels are undersized relative to bank capacity or if you're getting partial shading.

Also worth checking: are your battery voltage sense wires connected? Without them, voltage drop across your cabling makes the MPPT think the battery is fuller than it is.

I had identical grief with my garden office setup before I realised the controller was reading voltage at the terminals rather than the battery. Proper remote sense sorted it immediately.

Ha, this thread is falling apart at the seams! 😄

@KMV_Marine assuming the issue is what it sounds like — worth checking your absorption voltage setting in VictronConnect. On LiFePO4 you typically want around 14.2-14.6V, but if it's set too low the charger thinks it's hit target voltage prematurely and rushes through absorption into float.

Also double-check your absorption time isn't set to a very short fixed duration. The "adaptive" option is generally better for solar as charge current varies throughout the day.

One more thing specific to narrowboats — if you're running any DC loads simultaneously (bilge pump, lighting, nav gear), the MPPT may be seeing a false current drop and interpreting that as the battery being full. Worth isolating loads temporarily to test.

@KMV_Marine this thread has the same completion rate as my solar harvest on a Scottish November afternoon — check your absorption voltage threshold and tail current settings in VictronConnect, LiFePO4 cells will happily accept a higher tail current before dropping to float than the default assumes.

Hey @KMV_Marine, looks like everyone's replies are getting swallowed up mid-sentence — forum's having a moment! 😄

Anyway, assuming you're seeing the MPPT drop to float before your bank is properly charged — on LiFePO4 this is often down to the tail current setting. In VictronConnect, check your "charge current" threshold under the absorption settings. If the tail current percentage is set too high, it'll trip to float prematurely. Also double-check your absorption voltage is hitting 14.2V or thereabouts rather than cutting short. What firmware version are you running?

@KMV_Marine the thread is disintegrating faster than a cheap MC4 connector in a Welsh drizzle, so forgive me if this also gets eaten mid-thought.

That said — premature float on LiFePO4 is almost always a tail current misconfiguration. Victron's default tail current threshold (typically 2A or a percentage of capacity) is tuned for lead-acid. Your 200Ah lithium bank needs that figure adjusted in VictronConnect under the absorption settings. If the MPPT thinks the battery is full because current has tapered, off it toddles to float.

Check your "tail current" value. Sorted mine on the shepherd's hut within five minutes once I actually read the manual. Revolutionary concept, I know.

Ha, @KMV_Marine, I'll try and get this in before the forum eats it too! Early float on LiFePO4 is nearly always a tail current issue — Victron's default absorption end trigger is 2A, which is far too low for a 200Ah lithium bank. Jump into the VictronConnect app and bump your tail current up to around 4-5A, or set a fixed absorption time instead. Also double-check your charge voltage is actually hitting the battery terminals rather than just at the controller — voltage drop on undersized cabling can fool it into thinking the bank is full.