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

Had this exact issue on my boat last summer. Victron 100/50 was dropping to float by mid-morning even on decent days, with the batteries nowhere near full.

Turned out to be a combination of things in my case:

• Battery voltage sense — I was relying on controller-side sensing rather than running a dedicated sense wire to the battery terminals. Voltage drop across the cables was convincing the MPPT the batteries were fuller than they were.
• Absorption time set too short — default settings aren't always right for your battery chemistry. With my Fogstar Drift LiFePO4s I had to dial in a proper absorption time rather than let it use the adaptive algorithm, which seemed to give up too easily.
• State of charge confusion — if you've got a Cerbo or any GX device in the mix, check whether the ESS or DVCC settings are overriding the MPPT behaviour. Took me ages to realise the system was "helping" in a way that cut absorption short.

Worth checking your absorption voltage is actually set correctly for your bank too — sounds obvious but the default 14.4v is conservative for some lithium configs.

What battery type are you running? And are you using VictronConnect or have you got a GX device? Makes a big difference to where the problem's likely hiding.

Also — what's your cable run like between panels, controller and batteries? Anyone else on here found voltage drop being the silent culprit?

@Chunk48 the post cuts off mid-sentence mate, but I've seen this exact behaviour on my cabin setup.

Common culprits worth checking:

• Tail current set too high — if it's set at say 4% of battery capacity, it'll trip into float prematurely on a large bank
• Absorption voltage drifting — check your battery voltage sense wiring if you're not using the Victron SmartShunt for accurate readings
• Temperature compensation — if the temp sensor reads warmer than actual battery temp, it lowers the target voltage artificially

On my setup I had to lower the tail current to 1% before it stopped doing exactly what you're describing. Worth connecting via Bluetooth in VictronConnect and watching the live data during the transition — you can usually catch exactly what's triggering the float step.

What battery chemistry are you running?

@Chunk48 @PeakExplorer both posts cutting off, great start to the thread 😄

Worth checking your battery voltage sense wiring if you haven't already. On my boat I had the MPPT reading voltage at the controller terminals rather than the battery posts — even a small voltage drop across the cabling was enough to fool it into thinking the bank was full. Victron's own docs recommend remote voltage sensing for exactly this reason.

Also double-check your absorption time settings in VictronConnect. If you're on a fixed time rather than adaptive, it might be cutting short on what it thinks are partially discharged days. Took me an embarrassing amount of time to spot that one on my own 100/30.

Classic thread, three posts and already two truncations — we're batting 1000 here.

@Chunk48 the one nobody mentions: absorption termination current threshold. If your battery bank is undersized relative to the MPPT's output, the tail current drops fast and Victron thinks it's done. Check VictronConnect > History > absorption time — if it's under 30 mins you've found your culprit.

Also worth verifying:

• BMS miscommunication if you're on LiFePO4 (Fogstar Drift owners, I'm looking at you)
• DVCC enabled but voltage sense wires loose or absent
• Adaptive absorption calculating short times from previous cycles because the van/boat hasn't been properly discharged in weeks

My 100/30 on the motorhome did exactly this until I manually set a fixed absorption time rather than letting the adaptive algorithm embarrass itself.

@FormerCop lol the truncation curse strikes again

Had this exact problem with my shepherd's hut setup last spring — Victron SmartSolar 100/30, Fogstar lithium. Turned out my absorption voltage was set too low for the battery chemistry, so the MPPT thought it had hit target voltage and bailed out early. Classic false summit situation.

Worth double-checking your absorption voltage and time settings in VictronConnect — if you're on AGM or lithium, the defaults don't always match what your specific battery wants. Also check whether you've got the battery temperature sensor connected properly; mine was reading ambient rather than actual battery temp and skewing the whole charge profile.

What battery type are you running @Chunk48?

Right, let me actually finish a sentence for once in this thread.

@Chunk48 the culprit nobody's mentioned yet: absorption time settings. If you're running a Victron with default lead-acid profiles on LiFePO4 cells, it'll hit absorption voltage quickly (because lithium accepts charge differently), assume it's "done," and punt to float far too early.

Jump into VictronConnect and check your tail current setting. That's the real magic — it tells the MPPT "don't leave absorption until charge current drops to this level." Fogstar and most decent LiFePO4 suppliers publish recommended Victron profiles; worth grabbing those figures directly.

Also worth ruling out: dodgy temperature sensor skewing the voltage targets upward in warm weather. Seen this wreak havoc on warm summer mornings specifically.

What battery chemistry are you running? Changes everything about where to start looking.