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

Had this exact drama with my van setup last summer — Victron 100/30 decided my 200Ah Fogstar lithium was "full" by about 11am every day like it was clocking off for lunch.

Turned out my absorption voltage was set a touch low and the tail current threshold was doing the heavy lifting too aggressively. Bumped absorption up to 14.2V and dropped the tail current percentage in VictronConnect and it sorted itself right out.

Few things worth checking:

• Battery profile — are you on a preset or custom? Presets can be oddly conservative
• Tail current setting — if it's too high a percentage, it'll boot you to float before the battery's actually had its fill
• Temperature compensation — if you've got a temp sensor doing its thing in cold weather, it'll push voltages around in ways that look like early float
• State of Health on your battery — an older bank with degraded capacity fills up quicker than you'd expect

Also worth connecting via Bluetooth and watching the live data for a bit rather than just trusting the LED. The dashboard tells a much more honest story.

Anyone running AGMs having the same issue or is this more of a lithium quirk in your experience? My mate with a shepherds hut build swears his gel setup never does this but I'm not convinced he actually checks it properly.

@Chalky had almost the same thing on my motorhome last season. Worth checking your tail current setting — that's what tells the Victron when to end absorption and drop to float. Mine was set far too high (default I think), so it was seeing the battery accept less current and deciding it was full well before it actually was.

In VictronConnect you can set it as a percentage of your battery capacity. I knocked mine down significantly and it made a real difference to how long it stayed in absorption.

Also worth double-checking — is your battery temp sensor connected properly? If the Victron thinks the battery is warmer than it is, it'll adjust voltage thresholds downward and bail out of absorption earlier than you'd want.

What absorption voltage are you actually running it at?

@Chalky yeah this bit me too on my tiny house setup. The default absorption time on Victron is often way too short for LiFePO4 — it's basically tuned for lead acid assumptions.

Worth checking if you're running the adaptive absorption setting. Mine was calculating a short absorption window based on the previous day's bulk time, which sounds clever but can go wrong if you had a partly cloudy morning.

I ended up switching to fixed absorption time (about 20-30 mins is usually enough for LiFePO4 honestly) and setting the float voltage down to around 13.5V so it's basically just resting rather than actively charging.

Also — are you using the VE.Direct cable with the Victron app? The history graphs make it much easier to see exactly what the controller was doing and when it bailed out.

@Chalky this one's a classic. I spent a miserable fortnight in the Scottish Highlands last year watching my Fogstar 280Ah bank refuse to charge properly because my 100/50 was using the default lithium preset — which is frankly optimistic nonsense for real-world conditions.

The piece nobody's mentioned yet: battery temperature. Victron's MPPT will throttle absorption aggressively if it thinks the bank is warm, and if you've no temperature sensor fitted, it's guessing. Grab a Smart Battery Sense or at minimum wire up the VE.Smart network so your BMV-712 is actually talking to the controller.

Also check your absorption voltage in VictronConnect — if it's set even 0.1V low for your specific Fogstar cells, the controller hits target voltage faster than expected and bails early. Fogstar's own documentation gives recommended charge parameters worth matching precisely.

Had this on my narrowboat last winter — turned out my absorption voltage was set a touch low (3.45V per cell instead of 3.5V), so the Victron genuinely thought it was done when it wasn't even close.

Worth double-checking your battery profile in VictronConnect matches your Fogstar's spec sheet exactly — those two documents disagreeing is basically the root of all evil on LiFePO4 setups.

Also, if you're using a BMS with a charge-enable signal, make sure it's not accidentally telling the Victron to back off early via the VE.Direct port. My Fogstar Drift's BMS had me chasing ghosts for three days before I spotted that one. 🙈