Victron MPPT keeps dropping to float way too early — 280Ah lithium bank nowhere near full

Had exactly this with my shepherd's hut setup last summer. Turned out my absorption voltage was set a touch low — the Victron was hitting its target voltage too quickly under light load and calling it done. Bumped absorption up to 14.2V and extended the absorption time, made a huge difference.

A few things worth checking:

• Battery voltage vs controller voltage — are they actually the same? Volt drop across your cable run can fool the MPPT into thinking the battery is fuller than it is. Proper cable sizing matters more than people realise.
• Tail current setting — this is the one most people miss. If your tail current threshold is too high, the controller exits absorption early even if the battery isn't actually full. With a 280Ah bank you want that set quite low, maybe 2-3% of capacity.
• BMS communication — if you're running a Fogstar or similar with a BMS that's talking to the Victron via VE.Direct or similar, the BMS might actually be requesting the float transition. Worth checking what the BMS is telling it to do in VictronConnect.

What lithium cells are you running? Some of the budget LiFePO4 packs have quite flat charge curves and the MPPT can genuinely struggle to tell where you are in the state of charge. A proper battery monitor like a BMV-712 alongside the MPPT makes diagnosing this so much easier — you can actually see what SoC you're hitting when it drops to float.

What does your VictronConnect history graph look like? That'll tell us a lot.

@SophieHobbs74 yeah that's a classic one. Also worth checking your absorption time setting — if it's set too short, it'll bail out early regardless of voltage.

On my van build I run a Fogstar 280Ah and had similar grief. Bumped absorption time to 2 hours minimum and it sorted it. Victron's adaptive absorption can also get confused if your previous cycle was shallow — it "remembers" and shortens the next one accordingly.

Check the history tab in VictronConnect, look at how many Ah went in during absorption. If it's a small number relative to your bank size, that's your tell.

Had this exact drama on my narrowboat last season — turns out the tail current setting was the sneaky culprit nobody mentions.

On a lithium bank, if your Victron's tail current threshold is set too high (say 4-5% of capacity), it'll happily declare "job done!" and swan off to float while your cells are still gasping for that final 10-15%.

On my 280Ah Fogstar bank I dropped it to around 1-2% of capacity (~3-4A) and the difference was night and day — proper full charges every time.

In VictronConnect: Settings → Battery → Tail current — have a poke around in there before you go changing voltages all over the shop. @WonkyMechanic's absorption time point stands too, but sort the tail current first or you're just papering over cracks.

@RetiredChef nailed the tail current thing — on my motorhome's Victron SmartSolar I had it set to something daft like 4% which on a 280Ah bank means it exits absorption the moment draw drops below ~11A, so basically any sunny afternoon with nowt running. Drop it to 1-2% and suddenly your Fogstar cells actually get a proper top-up before it chickens out into float.

Great points all round here. One thing worth adding — have you checked whether you've got the battery capacity set correctly in VictronConnect? If Victron thinks your bank is smaller than it actually is, the tail current calculation gets thrown right off because it's working from a percentage of that figure. 280Ah is a decent bank and even a small error there compounds quickly. Also, @SophieHobbs74 — with lithium specifically, I'd suggest bumping your absorption voltage up to whatever your BMS manufacturer actually recommends rather than leaving it at a generic default. Victron's out-of-the-box lithium presets can be a bit conservative sometimes. Worth a look in the VictronConnect app under the battery settings — takes five minutes and might sort it completely.