Anyone else had their Fogstar Drift cells drift out of balance after winter storage?

Left my 280Ah LiFePO4 pack (4x Fogstar Drift 70Ah cells, Daly 100A BMS) sitting in the van over winter — maybe 3 months barely touched. Came back to it last week and one cell was sitting at 2.9V while the other three were around 3.2V. Not a disaster, but enough to trip the BMS low-voltage cutoff.

Did a slow top-up with my Victron IP22 charger, brought everything up gradually, and the cells did balance out eventually — took a couple of charge cycles. The Daly's passive balancing is pretty feeble at 35mA so it's slow going. Wondering whether this is just normal self-discharge variation between cells, or a sign that one cell is genuinely weaker than the others.

Has anyone added an active balancer alongside a Daly to speed this up? I've seen those cheap Chinese active balancers on Amazon — 1A or 2A versions — and I'm tempted. Or is it worth just upgrading the whole BMS to something like a JK with built-in active balancing? Would love to know what others have done before I start throwing money at it.

@PanelGraham 2.9V after storage is pretty typical with Daly BMS — the passive balancing is quite weak at the best of times, and if the pack sat at a low state of charge it likely just self-discharged unevenly.

Had similar with my boat setup after a quiet January. Fixed it by charging slowly to around 3.4V per cell then letting the BMS balance overnight — took a couple of cycles before they settled back together.

Worth checking whether that low cell has genuinely drifted or if it's just lagging. If it keeps dropping away from the others under load, you might have a weak cell developing.

If the Daly keeps struggling, an active balancer (cheap ones on Amazon, £15-20) wired across the cells makes a huge difference — particularly for storage scenarios.

@PanelGraham had something similar with my garden office setup last winter — one cell dropped noticeably lower than the others after about 6 weeks idle. Turned out my Daly was drawing a tiny parasitic current continuously, which accelerated the imbalance.

Worth checking:

• Measure the BMS quiescent draw with a clamp meter when everything's "off"
• Top balance the cells individually before reconnecting — I used a bench PSU set to 3.65V per cell
• Consider swapping to an active balancer alongside the Daly; picked up a cheap 4S one off Amazon and it's made a noticeable difference

Since that episode I now disconnect my pack properly before any extended period without solar input. The Fogstar cells themselves seem fine once rebalanced — I don't think it's a cell quality issue, more the Daly's limitations showing up during storage.

Seen this exact thing with my motorhome pack over last winter. Had a Daly on a 4-cell 280Ah setup and one cell crept down to 3.1V while the others stayed around 3.3V — nothing dramatic but enough to trigger low-cell cutoff at the worst moments.

What sorted it for me long-term was switching to a Victron SmartShunt so I could actually see what was happening over time, then eventually ditching the Daly for a JK BMS. The active balancing on the JK is a different world — it genuinely keeps the cells tight during storage without needing to be at full charge.

If you're not ready to swap the BMS yet, try top-balancing the cells manually before storage next autumn. Bring each cell individually to 3.65V with a bench power supply. Makes a noticeable difference to where they settle after months of nothing.

@PanelGraham worth checking whether that 2.9V cell has actually degraded or just self-discharged more aggressively than the others — LiFePO4 cells aren't perfectly matched in self-discharge rate, especially after a few charge cycles.

My approach on the static caravan pack (also Fogstar Drift cells, though I'm running a JK BMS with active balancing): I leave it at around 50-55% SOC before any extended storage. The JK's active balancer keeps things remarkably tidy even over months.

If you're sticking with the Daly long-term, I'd suggest doing a full slow top-balance before storage rather than leaving them wherever they land. Bring each cell individually to 3.65V via a bench power supply, then let them rest. That gives the passive balancer the smallest possible job to do over winter.

Also — has the Daly gone into sleep mode entirely? Some won't wake cleanly without a manual reset via the app.

Classic winter storage drama — my narrowboat pack pulled the same stunt last January, one rogue cell sulking at 3.1V while the others were perfectly fine.

What sorted it for me: slow top-balance at cell level before reconnecting to the BMS. Disconnect everything, charge each cell individually to 3.65V with a decent bench charger (I used a cheap CC/CV unit off Amazon), then reassemble. The Daly can mask how far out things actually are until you do this properly.

Worth noting: LiFePO4 self-discharge isn't equal across cells — manufacturing tolerances mean one cell will always be the weakest link, especially if storage temps dropped below 5°C over winter. @Cerbo_Geek is right to check for degradation, but in my experience it's usually just imbalance rather than a dead cell. A proper top-balance session should have you right again.