Anyone else finding their batteries struggling more than usual this winter?

Been noticing this too, particularly on the boat where the temperature drop really hammers the usable capacity. My Fogstar Drift LiFePO4s have built-in low-temp protection which cuts charging below about 5°C — sensible design, but it means the solar input just stops dead on a hard frost morning until the cells warm up naturally.

The physics is fairly unforgiving. Even good lithium cells lose a meaningful percentage of capacity as temperatures drop toward zero, and if you're running older AGMs the situation is considerably worse — lead-acid can lose 30-40% capacity in genuinely cold conditions.

A few things that have helped on my setup:

• Insulating the battery compartment — even basic closed-cell foam makes a noticeable difference overnight
• Allowing charge current to warm the cells gently before expecting full capacity
• Keeping batteries at a higher state of charge going into cold nights, since internal resistance rises sharply when depleted and cold

The solar side is actually fine — irradiance is obviously low but panels technically perform better in cold temps, so any decent sun we get is being harvested reasonably well. It's purely the storage side causing grief.

Running a Victron SmartShunt which lets me log historical capacity and the graphs through November and December tell an obvious story.

Curious whether anyone's tried active battery heating solutions — some of the newer cells have self-heating variants but I've not gone down that route yet. Also interested if those of you with ground-mounted systems are seeing better thermal stability than roof or vehicle installs?

What temperatures are you actually recording at battery level rather than ambient?

Yeah the low-temp cutoff is a double-edged sword isn't it. My panels are still generating on bright winter days but if the bank's too cold the BMS just refuses to accept charge — frustrating when you're watching good solar go to waste.

What's helped me is a small self-regulating heating pad wired to a thermostat relay, kicks in around 5°C and keeps the cells in the acceptable range. Draws very little and means I'm not losing charging windows.

Also worth checking your Victron settings if you're running one — the low-temp charge disconnect in DVCC can be configured to work alongside external heating rather than just cutting everything dead.

Location makes a big difference too. My setup is partially sheltered which helps retain overnight heat. A boat's probably far more exposed to ambient swings than most.

Really interesting thread — and something I've been grappling with at my static caravan setup too.

One thing worth adding: even above the low-temp cutoff threshold, LiFePO4 internal resistance rises significantly as temps drop, which means your BMS may allow charging but you're still pushing against degraded acceptance rates. I've noticed my Victron MPPT logs showing the batteries taking noticeably longer to reach absorption on cold mornings, even when charging isn't being blocked outright.

A battery heating mat wired through a simple thermostat can make a meaningful difference — keeps the cells above ~5°C without drawing excessive power. Worth considering if yours are in an exposed compartment.

@LakelandNomad — boat installations must be particularly brutal for this given the ambient temperatures near the hull. Are your Fogstars in an insulated battery box?

My van-to-EV charging setup has really highlighted this. The Renogy batteries are basically staging a sit-down protest below 5°C — "we're here, we're just not doing anything."

Quick question for the thread though: has anyone actually calculated what percentage of usable capacity they're losing at, say, 2°C vs a

Good thread. One thing nobody's mentioned yet is the benefit of using your battery bank itself as a thermal mass — if you can insulate the battery compartment well enough, the heat generated during charge/discharge cycles helps maintain a workable temperature even overnight.

In my van build I lined the battery box with 25mm Celotex and added a small 12v PTC heater element wired through a thermostat set to kick in at 5°C. Draws very little and keeps the Fogstar cells above the BMS cutoff threshold all night.

@PeakCamper the "sit-down protest" analogy is very accurate — I had identical behaviour last January parked up in the Cairngorms. Worth checking your Renogy BMS specs; some of them have a resume temperature several degrees above the cutoff, so recovery takes longer than you'd expect.

Relevant to both my shepherd's hut and the van actually. The hut is the bigger problem — it sits unoccupied mid-week so the batteries get properly cold before I'm even drawing from them.

What's made a noticeable difference is a small thermostatically controlled heat mat underneath the battery box, pulling from a tiny secondary cell that stays inside the insulated space. Sounds daft but it keeps the main bank just above the BMS cutoff threshold overnight.

@Tommo makes a fair point about thermal mass — I've started leaving a low background draw on the hut's heating circuit purely to keep temps up, rather than letting everything go stone cold between visits.

Does anyone know if Victron's low-temp charge disconnect settings can be tuned more granularly than the defaults? My MPPT seems quite aggressive about cutting off earlier than I'd expect.