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

Had this exact issue last summer with my 100/30 on the motorhome. Drove me absolutely mental for weeks.

Turned out my battery voltage sense was way off — the MPPT was reading voltage at the controller terminals rather than at the battery itself, so with any cable resistance it was seeing inflated numbers and thinking "job done, float time." Classic.

Few things worth checking:

• Proper voltage sensing — if you've got a BMV-712 or similar shunt, make sure you've enabled DVCC in VictronConnect and set the shared voltage sense. Game changer.
• Absorption time settings — are you using fixed or adaptive? Adaptive can behave weirdly if your batteries were already partially charged when you started the morning cycle
• Battery type config — sounds obvious but I had mine set wrong for months. Running LiFePO4 (Fogstar Drift 100Ah) with settings left over from the old AGM

Also worth checking the actual state of your batteries. If they're genuinely reaching float voltage quickly, maybe they're not depleting as much as you think overnight — or they're tired and not accepting charge properly.

What batteries are you running and what are your absorption voltage/time settings? Would help narrow it down. The VictronConnect history graphs are brilliant for diagnosing this — check if absorption duration is consistently short or just occasionally.

Victron's forums are decent too but half the answers there assume you've got a full-blown ESS installation rather than a simple van or cabin setup, which gets frustrating.

Anyone else got thoughts on this? Particularly curious if it's more common with certain battery chemistries.

@OffGridMax yeah the voltage sense issue is a classic one. If you haven't already, run a dedicated sense wire directly to the battery terminals — makes a huge difference, especially if you've got any length of cable between the controller and battery.

Also worth checking in VictronConnect whether you've got the battery type set correctly. If it's set to AGM but you're running lithium (or vice versa), the absorption threshold will be wrong and it'll drop to float miles too early.

Tail current setting is another one people miss — if it's set too high it'll exit absorption prematurely. I had this on my garden office setup with a Fogstar Drift 100Ah. Dropping tail current from 4% to 2% sorted it completely.

Check your VRM logs if you've got a Cerbo — the charge history graphs make it obvious what's happening.

@CE_Builds is right about the sense wire, but worth adding — even with proper sense wiring, the absorption termination current threshold is often the real culprit here.

In VictronConnect, check your tail current setting under the charger parameters. Factory default is often 1A or 2A, which on a larger LiFePO4 bank will trigger float transition embarrassingly early when the cells are genuinely only 70-80% full.

I had this exact scenario with my 150/35 feeding a 200Ah Fogstar Drift bank. Bumping the tail current to 4A and extending absorption time to a fixed 2 hours made an enormous difference.

Also worth checking: battery temperature. If your MPPT has the optional temp sensor fitted and the battery is cold, Victron's temperature compensation actively reduces the absorption voltage, causing premature float. Disable temp compensation if you're running LiFePO4 — it's designed for lead-acid chemistry.

@BarryWood raises a good point on absorption termination — worth clarifying for anyone troubleshooting this that the Victron MPPT's default tail current threshold (typically 2% of battery capacity) can be wildly inappropriate depending on your battery chemistry.

On my shepherds hut build with a Fogstar 200Ah LiFePO4, I had to dig into VictronConnect and manually set the absorption time override rather than relying on adaptive termination. The algorithm genuinely doesn't behave predictably with lithium if you're not using a Victron BMS for DVCC control.

Worth checking:

• VRM/VictronConnect logs — look at actual absorption duration over several cycles
• Battery temperature — cold cells terminate early legitimately
• DVCC settings if you have a GX device in the system

If you're running lead-acid, the adaptive algorithm should work, but only if your initial bulk readings are accurate — which loops back to what @CE_Builds said.

@PaulCross good summary there. One thing I'd add from my own setup — if you're running this for a garden office or somewhere with a fairly predictable daily load pattern, it's worth logging a few days of data via VRM before assuming it's a fault at all.

Mine was dropping to float "early" but actually the Fogstar batteries were just absorbing faster than expected once I sorted the wiring. Looked wrong on paper but the batteries were genuinely full.

Check your actual state of charge against what the MPPT thinks it is — if those match, it might not be a bug. VRM's historical graphs make this dead easy to spot.

Really useful thread, this one. Quick question for @PaulCross and @BarryWood — does the absorption termination behaviour differ much between lithium and AGM profiles in VictronConnect?

I've got a Fogstar 100Ah lithium in the motorhome alongside an older AGM for emergency backup, and I'm wondering whether running two separate MPPTs (one per battery) would be cleaner than trying to compromise on a single profile.

The voltage sense issue @OffGridMax mentioned rings a bell — I had something similar where the MPPT was reading a solid 0.3V higher than actual battery voltage due to a long cable run with no sense wire. Sorted it completely once I ran a dedicated sense pair directly to the battery terminals.

Worth checking cable cross-section too — undersized wire causes enough voltage drop to completely fool the controller.