Victron BMS tripping at 90% SOC — anyone else had this with LiFePO4?

Had this exact thing on my boat last summer. Turned out one of my cells was drifting high faster than the others — the BMS was seeing that cell hit its high voltage limit even though the overall pack wasn't anywhere near full.

Worth checking your cell voltages individually if you can. On my Victron setup I could see it through the app but you might need a proper cell-level monitor if yours doesn't show that detail.

A few things that sorted it for me:

• Top balancing the pack properly — mine had never been done right from new
• Dropping the charge voltage slightly in the Victron settings (I went from 3.65V/cell to 3.55V)
• Letting it sit at absorption for longer so the balancer had time to do its thing

The Fogstar cells I've got are generally solid but they do seem to need a decent top balance when first installed, more so than some others I've used.

Also worth checking your BMS firmware is up to date — Victron pushed an update a while back that changed how some of the protection thresholds behaved, caught a few people out.

What BMS model are you running exactly? And are you seeing any pattern — does it trip at the same time of day, or randomly? If it's always around midday when solar peaks that points more to a charge rate issue than a cell problem.

Anyone else had dodgy behaviour after a firmware update? Wondering if that's bitten more people than realise.

@MandyGrant that's almost certainly cell imbalance — exactly what I dealt with on my cabin setup last year using a Victron SmartShunt alongside a 280Ah Fogstar Drift pack.

Worth checking a few things:

• Top-balance the cells manually before trusting passive balancing to sort it
• In VictronConnect, log the individual cell voltages during charge — you'll likely see one rogue cell hitting 3.65V while others are still around 3.4V
• Reduce your absorption voltage temporarily (try 3.45V/cell) to give balancing circuitry more time to catch up

Passive balancers on most budget BMS units are painfully slow — sometimes only 50–100mA bleed current. If your cells have drifted significantly, that could take days of cycling to correct.

If it persists after a few cycles, a dedicated active balancer wired across the cells makes a dramatic difference.

@MandyGrant had the same drama with my van build last winter. One rogue cell was racing ahead of the pack every single charge cycle — BMS kept cutting out at what looked like 90% but was really just that one cell screaming at the ceiling.

What sorted it for me was dropping the charge voltage right back and letting the Victron's absorption phase do a proper slow top-up over several hours. Gave the passive balancing time to actually catch up rather than just waving at the problem as it flew past.

Worth checking your cell voltages individually during the final charge phase if you haven't already. A decent battery monitor will show you exactly which one's the culprit. Once I identified mine, a few careful balance cycles and it settled right down.

Classic top-balancing job waiting to happen — if your cells weren't properly balanced before first use, one will always sprint ahead and trip the BMS before the rest even get near full.

Worth checking your Victron BMS logs (via VictronConnect) to see which cell is spiking — if it's consistently the same one, you've got a drifter rather than a genuine BMS fault. Fogstar cells are usually pretty well-matched out of the box but they do drift over time, especially if you've had any partial cycles or uneven charging.

Temporary fix: drop your charge ceiling to ~54.4V (3.4V/cell on a 16S pack) and see if the tripping stops — buys you time while you manually top-balance. Done this twice on my motorhome setup and it's genuinely saved me from chucking packs I thought were dead.

@MandyGrant worth checking your Victron Connect app and looking at the individual cell voltages during charging — you want to catch exactly which cell is racing ahead and by how much. If the drift is only a few millivolts, a passive balancer on the BMS might sort it over several cycles. If it's more significant, you're probably looking at a proper top-balance session with a bench power supply, as @FormerCop suggests.

One thing I'd add that hasn't been mentioned — also check your cell interconnect busbar torque. A loose connection creates resistance which can cause false high readings on that cell tap. Caught me out on my narrowboat setup before I realised the actual balancing was fine. Simple thing to rule out before you start pulling the pack apart.

@FormerCop is right about the top-balancing, though I'd add one pedantic point — it's not just whether you balanced before first use, it's how accurately you did it. Even a few millivolts of difference between cells compounds over hundreds of cycles.

On my boat build I use a Victron Smart Lithium with cell balancing enabled obviously, but I also set my charge voltage slightly conservatively — 3.45V/cell rather than the full 3.65V. Means the pack never quite hits that point where a drifting cell trips things.

Worth double-checking your BMS cell voltage thresholds in Victron Connect too. The default high-cell cutoff is sometimes more aggressive than necessary for day-to-day use. You can dial it back a touch without compromising the pack's safety.