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

Had this exact issue last summer with my 100/30. Kept hitting float by mid-morning even on decent days, which made no sense with the batteries only sitting at maybe 60-70% SOC.

Turned out my absorption voltage was set too low — I'd just left it on the default Li profile but my Fogstar Drift cells wanted something slightly different. Worth double-checking your voltage settings against your battery manufacturer's spec rather than trusting the defaults.

Few other things worth checking:

• Battery temperature — if you've got a BMV or Smart Shunt with a temp sensor, make sure it's actually feeding data to the MPPT via VE.Smart networking. Mine wasn't paired properly and the temp compensation was doing weird things
• Tail current setting — this one catches people out. If your tail current % is set too high, it'll declare absorption done way before the battery's actually full
• Wiring resistance — voltage drop between controller and battery can fool the MPPT into thinking voltage is higher than it is

Spent an afternoon on VictronConnect going through all of it. The history graphs are brilliant for diagnosing — you can see exactly when it's transitioning and whether the absorption time looks right.

What battery chemistry are you running? Makes a big difference to where the issue might be. Lead acid and lithium behave completely differently when it comes to absorption termination.

Anyone else got thoughts on this? Curious whether it's more common with certain battery brands.

@JimKelly classic symptom of the tail current threshold being set too high. If your absorption tail current is set at say 4-5% of battery capacity, it'll drop to float prematurely when the panels are undersized relative to the bank — the controller sees the current naturally tapering off and thinks "job done."

Worth checking in VictronConnect under the charger settings. I had almost the same thing on my narrowboat setup with a 200Ah Fogstar lithium bank. Dropped the tail current to around 1-2% and suddenly absorption was actually doing something.

Also — what are your absorption voltage settings? If it's too low it'll cap out quickly as well. The two issues often compound each other and people only fix one half of the problem.

@JimKelly also worth checking if your battery voltage sense wires are connected — without them, the MPPT is guessing voltage at the controller terminals rather than the actual battery, and cable voltage drop can fool it into thinking the bank is fuller than it is. Victron's own VE.Smart networking sorts this brilliantly if you've got a BMV monitor knocking about, basically turns your whole system into one big happy family that actually talks to each other. Had this exact nonsense in my motorhome until I wired the sense properly and suddenly my Fogstar lithiums were actually getting a proper full charge rather than a polite suggestion of one.

@JimKelly one thing nobody's mentioned yet — check your absorption time setting isn't capped too low. In VictronConnect, under the charger settings, there's a "maximum absorption time" parameter. If that's set to something like 1–2 hours and your batteries are genuinely depleted, the controller will bail out to float regardless of tail current.

Also worth checking battery temperature if you've got a Smart Battery Sense or BMV with temp probe attached. A warm battery reads higher voltage at the terminals, so the MPPT thinks absorption is complete when it isn't.

I had almost identical behaviour on my narrowboat last spring with a 100/50 and Fogstar Drift LiFePO4 bank — turned out the Peukert exponent in the BMV settings was wildly wrong, confusing the whole system's SOC logic. Tightened that up and it sorted itself immediately.

Had this on my boat last season — drove me mad for weeks tbh.

What finally cracked it for me was realising my battery temperature was way off. Without a proper temp sensor, the MPPT was compensating voltage based on ambient, but my AGMs sit in an engine bay that runs warm. It was hitting the absorption voltage target earlier than it should've been.

Grabbed a Victron Smart Battery Sense and wired it up — made a noticeable difference straight away. VictronConnect showed the actual battery temp and the charge curves started behaving properly.

@MarineGeoff makes a good point about voltage sense wires too — both issues compound each other if you've got both problems at once, which I did 🤦

Definitely worth ruling out thermal compensation before digging deeper into the tail current settings.