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

Had exactly this with my 100/30 last summer. Turned out the absorption time was set too short in VictronConnect — it defaults to a fixed 2 hours but if your battery isn't fully charged by then it'll drop to float regardless. Worth checking whether you've got it on fixed or adaptive absorption.

The other culprit I'd look at is your battery temperature. I've got a Fogstar 200Ah LiFePO4 and when the SmartShunt SoC reading drifted slightly off, the MPPT thought the battery was fuller than it actually was and jumped to float prematurely. Syncing your SmartShunt with the MPPT via VE.Smart Networking sorted it for me — the controller then uses actual SoC data rather than just voltage to make that call.

A few things worth checking:

• What battery chemistry have you selected in VictronConnect? AGM profiles in particular have lower absorption voltages
• Are you using the built-in Bluetooth or a direct USB connection to configure it? I've seen odd behaviour when settings appear saved but haven't actually written properly over BT
• Any loads drawing during the absorption phase? That'll mask the current taper and confuse the controller

Also worth looking at your tail current setting — if that's set too high, it'll think the battery is full when it isn't. I had mine at 2A which was fine for a smaller battery but needs scaling to roughly 1–2% of battery capacity.

What controller model and battery setup are you running? That'd help narrow it down. Others on here have had similar with the 75/15 on smaller shepherd's hut installs too.

@SprinterProject worth also checking your battery temperature. My 100/50 was doing exactly this on my garden office setup last winter — kept dropping to float after barely an hour. Turned out the low ambient temp was throwing off the voltage readings and the controller thought absorption was done when it wasn't.

If you've got a Victron Smart Battery Sense or even just the temp sensor cable, it makes a noticeable difference. The adaptive absorption mode also helps — it calculates absorption time based on how long bulk took, so a cloudy morning means a longer absorption phase automatically.

Also double-check your absorption voltage is actually set correctly for your specific battery chemistry. Fogstar and most lithium suppliers include the exact figures in their docs and they're often different from Victron's defaults.

Been there with mine on the van. Spent a frustrating afternoon convinced the controller was faulty before I realised the absorption voltage threshold was set slightly below what my Fogstar batteries actually needed to trigger a proper absorption cycle.

Worth pulling up the charge history in VictronConnect — if you're consistently hitting float after 20-odd minutes, your battery voltage is likely touching the absorption setpoint almost immediately because it was never properly discharged to begin with.

Had a period last January where the van sat mostly unused and every "charge cycle" lasted about fifteen minutes. Looked alarming but was actually fine — shallow discharge, shallow recharge.

Check your actual absorption voltage setting against your battery manufacturer's spec first. Lot of people run Renogy panels into Victron kit and never bother cross-referencing the two sets of documentation.

Good points from @SprinterProject and @LisaHunt88 already — one thing neither has mentioned yet: check whether you've accidentally enabled BatteryLife mode in VictronConnect. It's designed for systems where you can't always fully recharge, so it deliberately restricts absorption to protect the battery long-term. Sounds counterintuitive but it'll drop to float early by design.

Also worth verifying your absorption voltage threshold is actually appropriate for your battery chemistry. A 12V LiFePO4 (Fogstar Drift, for instance) wants around 14.2–14.6V — if the threshold is set too low, the controller thinks it's done before it really is.

On my narrowboat setup I run adaptive absorption, which dynamically extends the absorption phase based on previous charge cycles. Far more reliable than fixed-time settings for variable solar days.

Had this exact nightmare with my shepherd's hut setup last winter. @DevonDweller makes a good point — but also worth checking your battery voltage readings in VictronConnect history. Mine was showing absorption completing "successfully" but the actual SOC was nowhere near 100%.

Turned out I had a dodgy connection on the battery negative causing a voltage drop — the MPPT was seeing a falsely elevated voltage at its terminals and thinking the battery was fuller than it was.

Tightened everything up, added proper lugged terminals (was using bare wire before, embarrassingly), and the issue vanished.

Also — are you using LiFePO4 or lead acid? The charge profiles are completely different and if someone's previously fiddled with the settings and switched battery type without resetting properly it can cause all sorts of weird behaviour.