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

Mine did exactly this last summer and I nearly threw the Victron out the window before realising my battery voltage sense wires had more resistance than my ex's attitude.

The MPPT reads voltage at the controller terminals rather than at the battery, so if your cable runs are even slightly dodgy — loose connection, undersized wire, a dodgy crimp you did at 11pm because "it'll be fine" — it'll see an artificially high voltage and bail into float before your batteries are anywhere near full.

Few things worth checking:

• Enable voltage sense via VictronConnect if you've got a SmartShunt or BMV in the mix — game changer
• Check your absorption voltage setting — mine had somehow drifted to 14.1V when my Fogstar Drift LiFePO4 wanted 14.6V
• Cable sizing — I was running 6mm² on a run that really wanted 10mm²
• Tail current — if your battery fills faster than expected, it should drop to float, so worth logging a full charge cycle and actually looking at the data rather than just vibing at it

VictronConnect's history tab will show you absorption time, which is the big tell. If it's dropping out after 10 minutes of absorption consistently, something's off with either your voltage calibration or the battery isn't actually as flat as you think going into the cycle.

Anyone else found the remote battery sense option made a dramatic difference, or is my setup just held together with optimism and cable ties?

@Tom1979 had the exact same issue with my cabin setup last year 😅

Worth checking a few things methodically:

• Voltage sense wires — as you found, any extra resistance here throws everything off
• Battery temp sensor — if it's reading ambient rather than actual cell temp, it'll compensate wrong and push float early
• Absorption time settings in VictronConnect — mine was set to adaptive and was behaving oddly with my Fogstar Drift lithium

Also double-check your battery voltage setting matches your actual bank. Sounds obvious but I had mine set 0.2V low after a firmware update reset everything silently. Drove me mad for weeks.

What battery chemistry are you running? AGM and LiFePO4 charge profiles are completely different and some Victron units don't always default sensibly after updates.

@Tom1979 classic voltage sense gremlin — but if you've already ruled that out, also check your absorption time settings in VictronConnect; the default "adaptive" algorithm calculates next-day absorption based on yesterday's tail current, so if your Fogstar cells have a low internal resistance they'll hit the tail current threshold suspiciously fast and the MPPT thinks "job done, float time."

Also worth verifying your battery capacity setting is correct — undersell it and the algorithm shortens absorption accordingly, which on a 48V LiFePO4 bank looks exactly like premature float but is technically working as intended (the pedant in me had to say it).

Set a fixed absorption time temporarily to isolate whether it's the algorithm or a genuine hardware/wiring fault before you start swapping kit.

@Tom1979 if sense wires are solid but it's still happening, check your tail current threshold in VictronConnect — if it's set too high, the MPPT thinks the battery's full when it's barely had a top-up, like calling it a night at 8pm.

Also worth logging via the VRM portal to see exactly when and why it's dropping — Victron's data is forensically detailed once you dig in. My motorhome setup threw identical strops until I realised my Fogstar lithium BMS was briefly pulling current during balancing, momentarily spiking apparent voltage and confusing the controller into thinking absorption was done.

Great thread, this caught me out last year too!

One thing nobody's mentioned yet — check your battery temperature compensation settings if you're running a BMV or Smart Shunt alongside the MPPT. If the temperature sensor is reading incorrectly (mine had a dodgy connection at the battery terminal), Victron will adjust the target voltage downward thinking the battery is warmer than it actually is. On a cool day that can shave a meaningful chunk off your absorption voltage and trick the system into thinking it's done far earlier than it should be.

Also worth enabling VE.Smart Networking if you haven't already — lets the MPPT pull voltage and temperature data directly from your battery monitor rather than relying solely on its own sense wires. Transformed the consistency of my charging cycles once I sorted that. @EmmaEdwards82 might find that useful for the cabin setup too!