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

Had this exact issue on my boat last summer. Victron SmartSolar 100/30, and it kept jumping to float after maybe 2-3 hours of absorption even though the batteries were nowhere near fully charged. Turned out my absorption voltage was set slightly too low for my Fogstar lithium cells, so the controller was seeing the resting voltage and thinking "job done."

Few things worth checking:

• Battery voltage sense — if you're only using the controller's internal sensing rather than a dedicated BMV or SmartShunt, voltage drop across the wiring can fool it
• Tail current setting — this is the big one for lithiums especially. If your tail current threshold is too high, it exits absorption prematurely
• Battery capacity setting — wrong Ah figure will confuse the adaptive charging algorithm

The VictronConnect app makes it dead easy to dig into this. Pull up the history tab and look at the absorption time across several days — if it's inconsistent and short, it's almost certainly the tail current or a dodgy voltage reading.

For my setup I ended up running a proper sense wire directly to the battery terminals rather than relying on the controller. Made a noticeable difference immediately.

Worth also checking whether you've got anything else pulling load during the charge cycle — on the boat I had the bilge pump kicking in occasionally which was muddying the current readings.

Anyone running a DVCC setup through a Cerbo GX? Curious whether that changes how this behaviour manifests, as I'm considering adding one for better system oversight.

Had this exact same headache with my garden office setup. Turned out my battery capacity setting was way off in VictronConnect — it was calculating the tail current threshold against the wrong Ah figure, so it thought absorption was "done" miles too early.

Worth double-checking your tail current setting. If it's set too high (like 2-4% of a wrongly entered capacity), it'll drop to float prematurely. I knocked mine down and it sorted it immediately.

Also — are you on AGM or lithium? If lithium with a BMS, sometimes the BMS is briefly throttling charge current and Victron interprets that dip as the tail current being hit.

What firmware version are you running? There were some absorption-related quirks on older builds.

@KevWatson57 worth checking your tail current setting in VictronConnect — this is the one people consistently overlook. The MPPT uses tail current as the primary trigger to exit absorption, and the default (4% of programmed battery capacity) is often wildly wrong if your capacity figure isn't accurate, or if you've got high parasitic loads running during charging that mask the actual current dropping off.

On my narrowboat I had to drop mine to around 1-2% before absorption duration became sensible. Also double-check whether you've accidentally enabled the BatteryLife algorithm — it deliberately curtails charging cycles to preserve battery longevity, which sounds exactly like what you're describing.

@Megan1996 makes a fair point about capacity settings too, both issues compound each other badly.

@FenlandSolar is absolutely right about the tail current — but I'd add that the default value is often far too high for larger battery banks.

On my shepherd's hut setup (200Ah Fogstar Drift lithium), Victron defaults to something like 2A tail current, which sounds reasonable until you realise that's 1% of capacity for a 200Ah bank. The correct figure varies by battery chemistry — my Fogstar documentation specifies 0.5% C10.

Worth checking in VictronConnect under Charger > Expert mode:

• Tail current — percentage of bank capacity, not fixed amps
• Max absorption time — a safety ceiling, not a target
• Absorption voltage — if this is too low, the battery never properly saturates and the controller gives up early

Also confirm your battery capacity is entered correctly in the app. I had mine set to 100Ah initially and the logic was completely skewed as a result.

@HighlandExplorer makes a good point about defaults being too high — worth noting that Victron's factory tail current is typically 4% of battery capacity, which is fine for AGM but will absolutely murder your absorption time with lithium.

On my narrowboat I run Fogstar Drift 200Ah cells and had to drop mine to around 1–1.5% before absorption ran a sensible duration. The logic is that lithium accepts charge so efficiently near the top that it hits the tail threshold almost immediately.

One thing nobody's mentioned yet: check your absorption voltage too. If it's set even 0.1V low, the battery reaches it quickly, sits there looking "full", and the tail current condition triggers sooner than it should. A miscalibrated BMV or battery monitor feeding voltage data back can compound this nastily.