Anyone else running Fogstar Drift LiFePO4 in a garden office through winter? Curious about BMS cut-off temps

Last October I finally swapped out the old AGM bank in my garden office for a 200Ah Fogstar Drift 12V. Brilliant bit of kit for the money — the Victron SmartSolar 100/20 plays nicely with it and the Bluetooth monitoring through the Victron app has been dead useful. Summer was fine, barely thought about it.

Now we're properly into the cold months and I'm getting occasional low-temp warnings when the office hasn't been heated overnight. Ambient was around 4°C one morning and the BMS cut charging until things warmed up — which is exactly what it's supposed to do, but it meant my loads were running purely from what was stored rather than topping up from the panels during the best part of the morning light.

I've got a small 300W oil-filled radiator on a timer to take the edge off before dawn, but that feels like a sledgehammer solution. Wondering if anyone's rigged up something more elegant — a thermostatically controlled heat mat under the battery, a battery box with insulation, anything like that. What temps are others actually seeing as the cut-off threshold on the Drift specifically? The datasheet says 0°C charge cutoff but I'm hitting warnings at 4°C which surprised me.

Hey @AndyButler, great choice on the Drift — I've had a 200Ah running my garden office since last February and it's been solid. Worth knowing the Fogstar Drift has a low-temp charge cutoff around 0°C built into the BMS, so on really cold mornings your SmartSolar might find itself blocked from charging until the cells warm up a bit. I added a small 12V heat mat underneath mine (the self-regulating type) which made a noticeable difference. Discharge down to around -20°C is fine though, so you won't lose power, just charging can stall. If your office has any residual heat from use during the day that helps enormously. What's your insulation like? Mine's a well-insulated timber frame so overnight temps inside rarely drop below 5°C even in January, which keeps things ticking along nicely.

Hey @AndyButler and @SarahLewis — I've got two of the 200Ah Drifts wired in parallel running my garden office and went through last winter with them. The BMS low-temp cut-off is around 0°C for charging, which caught me out a couple of times in January when the SmartSolar was throwing absorption errors first thing in the morning. Worth checking your battery temp sensor is actually connected properly to the Victron if you haven't already — made a huge difference for me. I also ended up boxing the batteries in with a bit of closed-cell foam insulation, nothing fancy, just keeps the ambient temperature around them a few degrees warmer overnight. Discharge seems fine down to around -10°C though, so you shouldn't lose your loads even on the coldest nights. What's your setup like for heating in the office itself?

Great thread! Just to add something that might not have come up yet — worth checking whether your BMS is cutting off charging or discharging (or both) at low temps. The Drift's BMS protects against charging below around 0°C, which is the critical one since pushing current into LiFePO4 cells when they're too cold can cause lithium plating and permanently damage capacity.

Discharging cutoff tends to be lower, around -10°C, so you'll likely still get power to your office even on a cold morning, just won't be able to top up until things warm a bit.

If your office is unheated overnight, @AndyButler and @EmmaPowell74, a small self-regulating heat mat on the battery can make a real difference in winter — keeps it above that charging threshold without drawing much. Some folks on here have done threads about that worth searching for. 👍

Great points all round here. One thing worth adding — have you lot looked into insulating the battery enclosure itself? I built a simple insulated box from 50mm PIR board around mine and it makes a noticeable difference keeping temps above that BMS charge cut-off threshold on cold nights. Doesn't need to be fancy, just reduces the thermal drop overnight.

Also worth mentioning that the Fogstar Drift's low-temp protection kicks in on charging not discharging, so you can still draw power fine — it's only when the solar tries to push charge in that you might hit issues. @AndyButler if your Victron is logging data, check the history for any absorption stage interruptions on cold mornings — that's usually the telltale sign the BMS has cut charging temporarily.