Victron MPPT keeps dropping to float way too early — is this normal?

Had exactly this with my Victron SmartSolar 100/30 when I first set up the garden office system. Spent a good week convinced something was faulty before I actually dug into the settings properly.

The culprit for me was the tail current threshold — it was set too high, so the controller was essentially deciding the battery was "full" before it genuinely was. Worth checking that first. In VictronConnect you'll find it under the charger settings; I dropped mine from the default and the absorption phase immediately extended to something sensible.

Also worth asking:

• What battery chemistry are you running? AGM, LiFePO4, and gel all behave differently and the defaults don't suit everything
• Are you on a preset profile or custom? Some of the presets are surprisingly aggressive
• Have you got a BMV battery monitor in the loop? Once I added a BMV-712, the MPPT started taking its charge state cues from the shunt rather than guessing — made a noticeable difference to how it handled absorption

My setup is a pair of Fogstar Drift 100Ah LiFePO4 batteries, and getting the tail current dialled in was genuinely the turning point. Before that, the controller was floating by mid-morning on a sunny day, which felt deeply wrong.

What batteries are you running and what does your absorption voltage look like in the live data? That'll probably tell us a lot.

@MarkGibson same thing caught me out on the boat. Turned out my absorption time was set way too short — Victron defaults can be a bit optimistic depending on your battery chemistry.

Worth checking your tail current setting too. If it's set too high, the controller thinks the battery's full before it actually is. Dropped mine right down and absorption time extended properly after that.

Also — what batteries are you running? If it's lithium you really want to make sure the BMS comms are sorted, otherwise the MPPT's just guessing. Had a Fogstar 12V 200Ah on mine and once I got the VE.Direct talking properly it made a massive difference.

@MandyGrant the default absorption settings catch so many people out. Worth adding though — if you're using lithium (Fogstar Drift or similar), early float transition can actually be intentional and correct behaviour. The issue is often that Victron's adaptive absorption algorithm calculates time based on the previous day's bulk duration, so on a cloudy day followed by a bright one it can be quite short.

On my narrowboat setup I had to dig into the Battery Preset and switch from adaptive to fixed absorption time to get consistent results. Also worth checking the tail current setting — if that's too high, it'll trigger float transition before the battery's actually full. VRM portal data is your friend here; the charge curve tells the whole story.

Great points all round. One thing I'd add that nobody's mentioned yet — have a look at your battery voltage sensing. If your MPPT is only doing internal voltage sensing rather than using the remote battery sense feature (the little two-wire connection to the battery terminals), it can read a falsely high voltage due to cable voltage drop and think the battery's fuller than it actually is. Victron Connect makes it dead easy to check — just look at whether it's showing "ext." or "int." for the voltage source in the app. Caught me out on my shed setup before I bothered running the sense wires properly. Once I sorted that, absorption ran the correct duration and the batteries actually got a proper full charge. Proper cable sizing helps too, obviously, but the sense wires are a quick win if you haven't already ticked that box.

Really good point from @Ollie1981 there on voltage sensing — that's often the culprit that gets overlooked. I'd also suggest checking your tail current setting if you're on lithium. The SmartSolar will drop to float once current falls below a certain threshold, and if that's set too high relative to your battery capacity, it'll cut absorption short even when the battery isn't actually full. In the VictronConnect app, dig into the expert settings and you can fine-tune it properly. Took me an embarrassingly long time to find that on my own setup. Also worth keeping an eye on the history tab — it'll show your absorption time over previous days, which helps you spot whether it's consistently cutting short or just occasionally, which points you towards different causes.

@Ollie1981 and @EdGrant91 have covered voltage sensing well so I'll add something different — check your tail current setting.

On lithium especially, if the tail current threshold is set too high the MPPT thinks absorption is done and drops to float prematurely. Victron's default is often calibrated more for lead-acid behaviour.

On my boat setup I dropped the tail current to around 1-2% of battery capacity and the early float issue disappeared completely. Worth logging a day's data via the VictronConnect app first so you can actually see what the current's doing at the point it switches — takes the guesswork out of it.

If you're on AGM the absorption time setting matters more, but tail current is where I'd start with lithium.