Static caravan solar setup – worth going lithium from the start or run AGM first?

Finally pulling the trigger on getting the static wired up properly. It's been running on hook-up whenever we visit, but we're losing the EHU pitch next spring and I want it fully self-sufficient. Roof space is decent – probably room for 4 x 200W panels without too much faff.

The question that's keeping me up at night: do I go straight to lithium (looking at Fogstar Drift 100Ah or maybe two of them in parallel) or start with a couple of AGM batteries and upgrade later? I've done the lithium route on the narrowboat with a Victron setup and honestly never looked back, but the caravan feels different – it sits unused for weeks at a time over winter and I'm not sure how lithium handles long periods of neglect at low state of charge.

The loads aren't massive – a 12V compressor fridge running 24/7 is the main draw, plus lights, phone charging, and occasionally a small inverter for a laptop. Rough estimate puts me around 60–80Ah per day in summer. Winter we barely visit so it almost doesn't matter, but I'd still want the system to survive sitting idle November through February without cooking itself.

Has anyone here run lithium through a proper UK winter in a static that's unoccupied for months at a stretch? Did you just leave it connected to a small trickle from the panels, or did you disconnect everything and store the batteries at partial charge?

Jonno71 | Posts: 847

@DerekDixon Go lithium from the off if your budget stretches to it, honestly. I made the mistake of starting with AGM on my cabin build thinking I'd "upgrade later" – ended up spending money twice and the AGM period taught me some frustrating lessons about state of charge management that I didn't need to learn.

The usable capacity difference is massive in real-world use. AGM you're really only working with 50% comfortably, lithium you're pulling 80-90% without any battery stress. For a static that might sit unused between visits, lithium handles partial states of charge far better too – your AGM will sulphate if it's left at 70% for three weeks, which happens constantly with holiday setups.

What sort of usage are you expecting – just lighting and a few devices, or are you wanting to run white goods as well?

WrongFuse | Posts: 312

@DerekDixon One thing worth factoring in that nobody's mentioned yet — static caravans can get properly cold over winter, and lithium batteries genuinely don't like charging below about 0°C without a low-temperature cutoff feature. If your van isn't heated between visits, a standard LiFePO4 bank could cause you grief from around November onwards.

Either budget for batteries with built-in low-temp protection (most decent ones have it now), make sure your BMS handles it, or consider where you're physically locating the batteries — somewhere that holds a bit of ambient warmth makes a real difference.

Doesn't change the overall advice that lithium is the better long-term choice, just worth planning around before you spend the money. What part of the country are you based? Makes a difference to how serious a concern it'll be.

DonnaMurray | Posts: 134

@DerekDixon I've gone through this exact debate for my shepherd's hut and ended up going straight to Fogstar Drift lithium — no regrets. The weight saving alone matters less for a static obviously, but the usable capacity difference is huge in practice, especially over winter when you're getting limited solar input. With AGM you're only safely using 50% anyway, so you're essentially buying twice the battery you can actually use. What's your rough daily consumption looking like? That'd help work out whether a smaller lithium bank would actually cover you vs a bigger AGM setup on paper.

BatteryJason | Posts: 1,203

@DerekDixon AGM is just paying twice — ask me how I know 🔋😭 Went Fogstar Drift 200Ah in the shepherds hut and haven't looked back; pairs beautifully with a Victron SmartSolar and you actually get the full capacity rather than AGM's "yes you can have 50% and be grateful about it" energy.