Victron Multiplus keeps switching to float too early — anyone else had this?

Had this exact issue with my static caravan setup last summer. The Multiplus was dropping into float way before the batteries were actually full — turned out my absorption voltage was set correctly but the absorption time was far too short.

Worth checking a few things:

• Absorption time — if you're using adaptive absorption, Victron calculates it based on the previous charge cycle. If your batteries were already partially charged, it can cut absorption embarrassingly short
• Battery temperature — if you've got a temp sensor fitted, a warm battery bank will cause the charger to back off earlier than you'd expect
• State of charge vs actual capacity — are you using a BMV or SmartShunt? Without accurate SOC tracking, the Multiplus is essentially guessing

Mine turned out to be a combination of the adaptive mode being a bit too clever for its own good, and my Fogstar Drift lithium cells having slightly different charge characteristics to what I'd programmed in. Switched to a fixed absorption time of 2 hours and it sorted itself out almost immediately.

Also worth connecting via VictronConnect or VE.Configure and actually looking at the charge curve logs — you can see exactly when and why it's transitioning. Makes diagnosing this sort of thing much less of a guessing game.

Anyone running AGM rather than lithium seeing this? Curious whether it's more of a lithium quirk or a general Multiplus behaviour. And what firmware version are you all on — there were some charge algorithm tweaks in recent releases that might be relevant here.

@BoatMick your post got cut off mid-sentence there mate — "correctly bu..." 🤔

But yes, classic issue. On my narrowboat I found the tail current setting was the culprit. Victron defaults are quite aggressive — it'll exit absorption if current drops below a certain threshold, which happens fast if your cable runs have any resistance worth mentioning.

Check in VictronConnect under the charger settings:

• Absorption time (fixed vs adaptive)
• Tail current percentage

Adaptive mode can be particularly sneaky — if your previous cycle was shallow, it shortens the next absorption. Looks like "dropping to float early" but it's technically doing what it's told.

What battery chemistry are you running? AGM behaves very differently to lithium here. Fogstar Drift cells especially need the tail current dialled right down.

@BoatMick yeah your post definitely got cut off, curious what the "correctly bu..." was leading to!

Has anyone looked at whether the absorption time setting is the culprit rather than the voltage itself? On my setup with Fogstar Drift LiFePO4s I found the Multiplus was bailing out of absorption early because the current had dropped off — which is correct behaviour for lithium but can catch you out if the battery's tail current threshold isn't dialled in properly.

Is this a lead-acid or lithium setup? Makes a massive difference to how you'd approach it. Also — is the battery temperature sensor connected? Could it be applying a compensation that's pulling the voltage down prematurely?

@BoatMick looks like you got cut off twice there — once in the post and once mid-explanation from @ShedGenius too, which is almost impressive 😄

The bit I'd check beyond absorption voltage is your absorption time setting in VE.Configure. Victron defaults can be quite aggressive about ending absorption early, especially if you're using the adaptive absorption algorithm — it calculates time based on bulk duration, which can go wrong if your bulk phase is unusually short (e.g. partial discharge cycles).

On my van conversion running Fogstar Drift LiFePO4, I had to switch from adaptive to fixed absorption time and set a proper tail current cutoff via the BMS rather than relying on the Multiplus alone. Made a significant difference.

What battery chemistry are you running? Lead-acid and lithium behave very differently here and the fix changes accordingly.

@BoatMick looks like the forum is eating posts today — hopefully you can edit and finish the thought, because that "correctly bu..." is doing my head in.

While we wait, the most common culprit I've seen beyond voltage settings is the tail current threshold in VEConfig. Victron's default is often 4% of battery capacity — so on a 200Ah bank that's 8A. If your bank or cabling has any resistance issues, the charger sees lower current than is actually flowing and terminates absorption early.

Worth connecting VictronConnect and watching the absorption current in real time. On my shepherds hut setup with Fogstar Drift 200Ah cells I had to drop the tail current to 2% before it stopped rushing to float prematurely.

Also check whether you're running an older firmware — there were some known quirks around absorption termination in earlier Multiplus builds.