Anyone else had grief with Fogstar Drift cells balancing at low SOC?

Picked up four 280Ah Fogstar Drift cells back in March to build a 24V 280Ah bank for the garden office. Spent a good while top-balancing them before assembly, got them all within 2mV at 3.65V, felt smug about it. Running them through a Daly 100A BMS with a Victron SmartSolar 100/30 doing the charging.

Everything was fine through summer, but now the days are shorter I'm regularly cycling down to 20–30% SOC and I'm noticing one cell consistently lagging behind by 40–60mV when they're down in that 3.1V range. The Daly is logging it but obviously won't trigger LV disconnect until 2.8V per cell, so no drama yet — just not loving the trend.

Has anyone bottom-balanced or done a capacity test on individual cells to isolate a weak one? I'm wondering if I got a dud in the batch or if this is just normal variance that's more visible at low SOC. Also open to whether swapping the Daly for something like a JK BMS with active balancing would actually help here or just paper over the cracks.

@FormerMariner24 yeah had exactly this with my garden office setup. Top balance looks immaculate then somewhere around 20-30% SOC one cell just decides to wander off.

Worth checking your BMS balance threshold — if it's only activating balancing above say 3.4V it won't touch the cells when they're low and drifting. I dropped mine to trigger at 3.3V and it helped a lot.

Also, are you running passive or active balancing? Passive on a 280Ah bank is basically doing nothing useful at low SOC, the currents are tiny. A small active balancer (I chucked a generic 2A one on mine) made a noticeable difference within a few cycles.

The Drift cells seem fine overall — mine are still within 8mV after about 8 months of daily cycling. Just needed a bit of coaxing early on.

@FormerMariner24 curious what BMS you're running and what your low-voltage cutoff is set to? I've got a similar shepherd's hut build in planning with Fogstar Drift cells and this is exactly the kind of thing I'm trying to get my head around before committing.

Specifically wondering — does the cell divergence at low SOC actually cause the BMS to trip prematurely, or is it more of a cosmetic annoyance in the app? And does it self-correct once you cycle back up through a full charge?

Also @WattHamish did yours settle down after a few charge cycles or did you end up having to intervene? I've seen some mention that Drift cells need 10-15 cycles before they really bed in properly, but not sure if that's genuine or just forum mythology at this point.

@FormerMariner24 classic case of cells that passed their top-balance MOT but forgot to revise for the bottom-end exam — mine did the same on the boat until I let the Victron Smart BMS actually learn the pack through a few proper full cycles rather than babysitting it with early absorption cutoffs.

@FormerMariner24 I had almost identical grief with a different brand but same story — cells that looked perfectly matched at the top diverged noticeably once I started pushing into the lower 20% regularly. What sorted it for me was doing a proper bottom balance as well, which I know sounds like extra faff but genuinely made a difference to cell tracking at low SOC. Also worth checking whether your BMS passive balancing is even active at lower voltages — some only kick in above a certain cell voltage threshold, so they're doing nothing useful when you actually need them. What's your typical daily depth of discharge? If you're regularly cycling deep rather than just occasionally, the divergence tends to compound over time. Give @Jock30's question about your LVC settings some thought too, that's quite relevant here.