Anyone else's Fogstar Drift cells getting warm just from sitting idle?

Noticed my 3x Fogstar Drift 100Ah cells are sitting at around 28°C in the static van even when the Victron SmartSolar has been idle overnight — no load, no charging, just... warm.

BMS is a Daly 100A, SOC hovering around 85%, ambient outside is maybe 12°C. Doesn't seem right that there's a 16-degree delta doing absolutely nothing.

Checked all the bus bar connections and nothing's loose, so I'm not pointing the finger at resistance heating. Wondering if the Daly is drawing more parasitic current than I thought, or if these particular cells just run warm at higher SOC?

Anyone measured their idle cell temps with a proper thermal camera — and is 28°C actually fine and I'm just being paranoid about my expensive rectangles?

DougLamb64 | 847 posts

@KentCruiser That's worth keeping an eye on but I wouldn't panic just yet. 28°C is within normal bounds for LiFePO4 — they do retain heat and ambient temperature in a static van can creep up more than you'd expect, especially if there's any sun on the bodywork.

That said, I'd double-check your BMS balancing isn't silently running in the background — some units will trigger a balancing cycle even at rest if cells are slightly mismatched, which generates a little warmth.

Also worth ruling out whether that's genuinely cell temperature or just the probe placement picking up ambient. What BMS are you running? You cut off mid-sentence there! Makes a difference knowing what telemetry you're actually working with before drawing any conclusions.

Compo27 | 312 posts

@KentCruiser Worth checking what your ambient temperature actually is inside the van first — if it's a warm day and the van's been sitting in sun, 28°C on the cells might just be the van itself being warm rather than the cells generating heat. Lithium cells do have a very small self-discharge current but nothing that should produce noticeable warmth on its own.

That said, I'd be more curious about your BMS — you didn't finish mentioning which one you're running. Some cheaper units can draw a surprising amount of parasitic current and actually generate a bit of warmth themselves which conducts into the cells. Worth putting a clamp meter on the negative to see if anything's drawing current overnight when it shouldn't be.