Anyone else noticed Fogstar Drift cells running warmer than spec in a garden office setup?

Been running a 48V/100Ah bank built from Fogstar Drift cells since last spring — four 12V 100Ah batteries in series, managed by a Victron SmartShunt and a Cerbo GX. The office pulls maybe 400–600W during the day (monitors, NUC mini PC, a small fan heater on eco mode in winter). Overall I've been dead chuffed with the setup, but I've clocked something that's nagging at me.

During heavy charge cycles on warm days — we're talking anything above 22°C ambient inside the office — the cells are sitting 4–5°C above what I'd expect based on Fogstar's published figures. Not into dangerous territory, but my Cerbo is logging consistent 31–33°C cell temps when I'd expect to be closer to 27–28°C. The BMS hasn't thrown any warnings yet, but I've read enough threads on here to know thermal runaway starts with "it was fine until it wasn't."

Has anyone else seen this with the Drift cells specifically, or is this more a symptom of poor airflow in a smallish insulated timber building? I've got a 140mm PC fan on a Shelly plug set to kick in at 29°C, but wondering if I need to rethink placement entirely — maybe get the bank off the floor and onto a shelf to improve air circulation underneath.

Curious about this @48VGal — are the cells themselves running warm or is it the BMS getting toasty? On my narrowboat I've found the Drift cells behave quite differently depending on airflow around them. Boat bilges are notoriously stuffy and mine were reading higher than I'd expect until I sorted some ventilation.

Also worth checking — what's your charge current set to on the Victron side? If you've got the absorption voltage slightly high for 48V it can push more heat into the cells than necessary. What does the SmartShunt show for charge current during peak solar hours?

Is your bank in an enclosed cabinet inside the office or relatively open? That seems like it could be a significant factor before concluding it's a cell spec issue.

Hey @48VGal — worth checking your cell interconnects and busbars first before assuming the cells themselves are the culprit. Loose or undersized connections create resistance that generates heat, and it's easy to overlook. Also, what's your typical charge rate? If your solar or charger is pushing them hard during the morning bulk phase, 400–600W draw on top of charging can stress them more than you'd expect in a confined garden office space with limited ventilation.

What does your Cerbo GX show for charge/discharge currents at the time you're noticing warmth? That data would really help narrow it down. The Drift cells are generally solid — I've not heard widespread complaints about them running hot under normal conditions — so I'd lean towards an installation factor rather than the cells themselves being problematic.