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

Had exactly this on my static with a Victron SmartSolar 100/30. Drove me absolutely mad for about three weeks before I tracked it down.

The culprit in my case was the tail current setting being too aggressive. Victron defaults it to 2A, but if your battery capacity is large enough, the charger interprets a relatively normal absorption current as "battery full" and kicks into float prematurely. On a 200Ah LiFePO4 (Fogstar Drift cells), 2A tail current was triggering float at roughly 70–75% SoC.

A few things worth checking:

• Tail current % — set it relative to your actual battery capacity (typically 1-2% of C is sensible)
• Absorption voltage — if it's set slightly low, the battery never properly saturates and the MPPT gives up early
• Battery temperature — if you're using a Victron BMV or SmartShunt, check whether temperature compensation is dragging your voltage targets down
• Parasitic loads — anything drawing current during absorption can confuse the controller's tail current calculation

Worth connecting via VictronConnect and watching the live graphs during a charge cycle. The history tab is useful but it doesn't give you the granularity you need to catch this in real time.

Also check whether you've accidentally enabled BatteryLife mode — that algorithm deliberately limits SoC if it thinks your solar yield is insufficient, which catches a lot of people out on partial-shade days.

Anyone running AGM rather than lithium might find the absorption time settings are the bigger issue — fixed time vs voltage-based termination behaves very differently depending on your bank size.

What battery chemistry are you running, and what does your VictronConnect

@BatteryTony classic one that catches people out. Worth also checking your absorption time settings if you're running a fixed-time profile rather than adaptive — on my narrowboat setup with 200Ah of Fogstar Drift LiFePO4, I found the Victron was dropping to float before cells had properly balanced because absorption time was set far too short for the battery capacity vs. panel wattage ratio.

Also worth ruling out high resistance connections — a dodgy crimped lug between battery and MPPT can fool the controller into thinking voltage has risen sufficiently when actually it's just seeing inflated readings due to resistance drop. Grabbed my clamp meter and found exactly that on my bow thruster cable run last winter.

Have you tried enabling the Battery Life algorithm off and going fully manual? Sometimes the adaptive mode gets itself into odd states and a reset sorts it.

Picking up on what @BatteryTony and @ExSquaddie49 have touched on — had something similar on my garden office setup last winter. Turned out my battery temperature was the hidden villain. The SmartSolar was reading ambient via the VE.Smart network from a sensor on the other side of the shed, so on cold mornings it was compensating aggressively and cutting absorption short because the voltage looked "high enough" once temperature-corrected.

Worth connecting a Smart Battery Sense directly to the terminals if you haven't already — mine was a game-changer. Also, are you using LiFePO4 or AGM? The default Victron charge profiles for AGM can be surprisingly optimistic about what counts as "full." What does your VictronConnect history graph actually show for the absorption duration — is it consistently short or intermittent?

Had this exact problem on the boat last winter. Turned out my battery temperature was the issue — Victron's temperature compensation was kicking in and dropping the absorption voltage threshold sooner than expected because the sensor was reading incorrectly.

If you've got a SmartSense or the built-in temp sensor on the battery, check it's actually registering realistic values in the VictronConnect app. Mine was reading 4°C warmer than actual, so the controller thought absorption was done when it wasn't.

Also worth checking whether you've accidentally got BatteryLife enabled — that algorithm deliberately curtails charging cycles and people often don't realise it's switched on. Not always what you want, particularly on a boat where you need proper full charges to keep lithium cells balanced.