24 Volt Charge Settings

Been wrestling with this one for my shepherd's hut setup and thought it worth throwing open to the floor.

My Victron SmartSolar is currently set to 28.4V absorption for the 24V LiFePO4 bank (Fogstar cells, 8S configuration). Manufacturer spec allows up to 28.8V ±0.4V, but I've been deliberately sitting under that ceiling — partly out of caution, partly because everything I've read suggests LiFePO4 really doesn't need to be pushed to the top of its voltage range to achieve a full state of charge.

The flat discharge curve these cells have means the difference between 95% and 100% SOC is genuinely tiny in practice. For a shepherd's hut that's occupied seasonally, I'd rather err on the side of cycle longevity than squeeze out that last sliver of capacity.

What I'm less sure about is whether consistently charging below the manufacturer's recommended ceiling causes any calibration drift over time — particularly with BMS SOC reporting. Mine occasionally reads oddly after a string of overcast days, and I wonder if the two things are connected.

A few questions for the collective wisdom here:

• Are any of you running 24V LiFePO4 banks at the full 28.8V, and have you noticed any degradation?
• Is there a sweet spot most people have settled on?
• Does your BMS manufacturer say anything specific about SOC accuracy when you're consistently not hitting the top absorption voltage?

Curious whether this is a genuine concern or one of those rabbit holes that sounds important but doesn't really matter in the long run. Would be especially useful to hear from anyone running Fogstar or similar prismatic cells in a similar arrangement.

@MPPTGal — 28.4V (3.55V/cell) is slightly aggressive for a stationary shepherds hut application where longevity matters more than squeezing every last amp in.

For my own hut bank (Fogstar Drift 24V) I've settled on:

• Absorption: 28.0V (3.50V/cell)
• Float: 27.2V (3.40V/cell)
• Tail current: 2% of capacity to exit absorption early

The BMS will protect against genuine overcharge, but repeatedly pushing cells to 3.55V accelerates degradation over thousands of cycles. Dropping to 3.50V costs you maybe 1–2% usable capacity but meaningfully extends cell life.

Also worth checking whether your Fogstar BMS documentation specifies a recommended charge voltage — some do, and it'll override any general LiFePO4 advice you find online.

What capacity is the bank and what's your typical daily consumption?

@MPPTGal — I'd agree with @BordersExplorer that 28.0V (3.50V/cell) is a sensible absorption target for a permanent installation where you're prioritising longevity over squeezing out every last amp.

For float, I'd go no higher than 27.2V (3.40V/cell) — some folks run even lower at 26.8V with no issues.

One thing worth checking is your absorption duration as well as voltage. Even at 28.0V, sitting there for hours is unnecessary with LiFePO4 — the charge curve flattens so quickly that a short fixed time absorption (say 30 mins) or a tight tail current cutoff will serve the cells much better than a lengthy CV phase.

What's your battery capacity and typical daily solar input? That'd help dial in the recommendations a bit more precisely for your specific setup. 🙂

Something I learned the hard way with my own Fogstar Drift bank — the tail current setting matters just as much as the absorption voltage itself.

Even if you nail 28.0V or 28.4V, if your Victron is sitting in absorption for 2 hours by default, you're stressing the top end unnecessarily. On a stationary setup like a shepherd's hut, I'd drop absorption time right down and let the tail current (say 2% of capacity) do the work of ending the stage early.

My SmartSolar now rarely spends more than 15-20 minutes in absorption once the bank is reasonably healthy. Far gentler on the cells long-term.

Worth digging into the Victron Connect advanced settings if you haven't already — it's where the real tuning lives, beyond just the headline voltage numbers.

Jumping in to add — for a fixed install like a hut, float voltage is often overlooked but really matters. I run 27.2V float (3.40V/cell) on my garden office bank and the Fogstar cells have been happy for two years now.

Also worth checking: if your SmartSolar is set to equalisation mode by default, disable it entirely for LiFePO4 — it'll cook the cells. Caught mine doing this ages ago, no idea how long it had been running.

@MPPTGal one other thing — are you using the VE.Smart networking with a BMV shunt? Linking them means the MPPT charges based on actual battery voltage rather than panel-side readings. Makes a noticeable difference, especially with longer cable runs.

Really useful thread this — just been through exactly this for my motorhome backup setup.

One thing nobody's mentioned yet: temperature compensation. If that shepherd's hut gets cold in winter (and they do!), your Victron's temperature sensor becomes worth its weight in gold. LiFePO4 doesn't actually need temperature compensation the way lead-acid does, but more importantly — does your BMS cut charging below 0°C? Worth checking your Fogstar Drift specs on that.

Also, @KentVanLifer's point about tail current is spot on — what figure are you actually using? I settled on 2% of capacity for my bank and it made a noticeable difference to how consistently the cells balanced.

For a fixed install that's not cycled hard daily, keeping absorption voltage on the conservative side (closer to 28.0V as @WendyLewis suggests) will pay dividends long-term. No need to push it.