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

Had this exact issue on my narrowboat last summer. Victron Multiplus II kept hitting float after maybe 45 minutes of bulk charging, battery SOC was nowhere near where it should've been.

Turned out my absorption voltage was set correctly but the absorption time was on the default "adaptive" setting, which was behaving oddly with my Fogstar Drift lithium cells. The BMS was occasionally sending a signal that the Victron interpreted as "batteries satisfied" when they weren't.

A few things worth checking:

• Absorption time — are you on adaptive or fixed? Try switching to fixed and see if it holds longer
• Battery temperature — colder temps can confuse the algorithm; do you have a temp sensor fitted?
• BMS communication — if you're running a managed lithium setup, is anything on the DVCC side interfering?

I ended up disabling DVCC temporarily as a test and the charging behaviour immediately improved. Wasn't a permanent fix but it confirmed where the fault was. Eventually sorted it by tweaking the CVL settings being sent from the BMS.

What batteries are you running? That makes a big difference to how you'd approach this. Lead acid vs lithium behaves completely differently with the Multiplus adaptive charging logic.

Also — have you got VRM or a Cerbo GX logging the charge curves? Being able to see the voltage and current graph over time made diagnosing this so much easier. Without that I'd have been guessing for weeks.

Interested to hear if others have seen this with different battery chemistries — wondering if it's more of a lithium-specific quirk or whether AGM users are hitting it too.

@OakSeeker — turned out your what? Don't leave us hanging like a Victron stuck in absorption! 😄

But seriously, classic culprit is dodgy battery voltage sensing — if the Multiplus is reading a false high voltage at the terminals, it'll think the batteries are happier than they actually are. Loose or corroded sense w

Classic case of the Multiplus trusting its internal current sensor more than reality — check your battery temp sensor cable first, because a dodgy NTC reading will convince the charger the batteries are warmer than they are and it'll bail out of bulk sharpish.

Also worth pulling up VRM or VictronConnect logs to see what voltage/current the unit thinks it's seeing at the point it drops — if bulk is ending before the absorption voltage is even reached, you've almost certainly got a wiring resistance issue causing voltage drop at the battery terminals versus what the Multiplus measures.

My static caravan setup did exactly this until I ran proper 70mm² cable with decent lugs rather than the optimistic 16mm² the previous owner bodged in.

@OakSeeker finish your sentence, some of us are actually waiting for useful information here.

Had something similar on my boat last year. Turned out the issue was the absorption time being set too short in VEConfigure — the "adaptive absorption" algorithm can get confused if your previous charge cycles were truncated for whatever reason. It basically learns the wrong thing.

Worth checking your charge curve settings in VEConfigure before assuming hardware fault. Also — what's your battery chemistry? If you're on lithium with a BMS that's been throttling current without the Multiplus knowing, it'll see reduced amps and think absorption is done when it isn't.

@Rob1963 makes a fair point on the temp sensor too, though I'd look at VEConfigure first. Simpler fix.

@OakSeeker the suspense is killing me too! 😄

While we wait — worth checking your VEConfigure settings for the "tail current" threshold. If it's set too high (say 4-5% of battery capacity), the Multiplus thinks the battery is full because absorption current has dropped to that level, even if SOC is still low. Happens a lot with larger lithium banks where the BMS is doing its own thing.

Also — are you running VE.Smart Networking? If your BMV-712 or SmartShunt is feeding SOC data back, sometimes a misconfigured charge efficiency factor throws everything off.

What battery chemistry are you on? LiFePO4 behaves very differently to AGM in terms of how quickly current tapers during absorption, which can fool the Multiplus badly if your profile hasn't been tuned properly.

@OakSeeker while we're all waiting for you to finish that sentence, I'll wager it's your absorption voltage threshold set too low — if the Multiplus thinks it's hit absorption target voltage under load, it'll happily trot off to float like it's done a full day's work.

Check VEConfigure: Absorption voltage, Tail current (the % of bulk current that triggers float), and crucially battery capacity (Ah) — undersized Ah setting means the tail current threshold is hit far too quickly.

Had this myself with my Fogstar Drift LiFePO4s; tail current was set for my old lead-acid bank and the Multiplus was essentially declaring victory at half time. Two minutes in VEConfigure sorted it completely.

@Rob1963 is right that the temp sensor can skew voltage targets too — worth ruling out.