Off-grid car battery trickle charger - Orion XS

Been mulling this one over for a while, actually. My static caravan setup runs a fairly beefy Victron system — 400Ah of Fogstar Drift LiFePO4 and a decent solar array — and I've occasionally wondered whether I could use it to keep my car battery topped up when it's sat on the drive for extended periods. Winter months especially, when the old Volvo barely moves for weeks at a time.

The Orion XS seems like the obvious candidate given I'm already deep in the Victron ecosystem, but I'm a bit sceptical about using a DC-DC charger designed for vehicle-to-vehicle charging as a static maintainer. It feels like using a sledgehammer to crack a nut, frankly.

A few questions worth throwing out there:

• Has anyone actually configured an Orion XS in a static/standalone mode rather than vehicle-to-vehicle?
• What are the actual quiescent draw figures when it's in float/storage mode? Because if it's quietly draining my leisure bank overnight, that defeats the purpose entirely
• Would a simple Victron Blue Smart IP65 just be a more sensible solution here, powered from the caravan's inverter or a dedicated 230V outlet?

The car sits for maybe 3–4 weeks at a stretch sometimes, and a standard lead-acid starter battery doesn't love that. I could just buy a CTEK, stick it on a timer, and be done with it — but I'd rather integrate it properly if it's worth the bother.

Anyone else running something similar off their off-grid bank? Genuinely curious whether this is elegant system design or just unnecessary faff.

@FormerTeacher the Orion XS is genuinely excellent for this — I've got one on the boat doing exactly this job, feeding a starter battery from my house bank. The key thing most people miss is setting the absorption and float voltages correctly for your specific chemistry rather than leaving it on defaults. With Fogstar cells you'll want to check their recommended charge profile and programme it in via VictronConnect. Also worth enabling the engine-running detection if you're doing any vehicle-to-van charging, though obviously less relevant for a static setup. One gotcha: make sure your cable sizing accounts for the full rated current over the actual run length — undersized cable kills efficiency fast.

Interesting use case — I've been down a similar rabbit hole for the garden office setup.

One thing worth factoring in alongside the Orion XS is whether your Fogstar Drift BMS will actually allow charge from a second source simultaneously. Most LiFePO4 BMS units handle it fine, but it's worth checking the parallel charging behaviour if your Victron MPPT is already pushing amps in.

Also, have a look at the Orion XS input voltage range — if your car battery dips below ~11.5V under load, the unit will cut out. Fine in most cases, but something to be aware of if you're running other car accessories at the same time.

@ForestBoater — does yours hold steady when the engine's off, or do you tend to leave it engine-running only?

@FormerTeacher worth being clear about what the Orion XS is actually doing in this context — it's a proper DC-DC converter with galvanic isolation, not just a passive connection. That matters a lot with LiFePO4 because it'll respect the charge profile rather than just dumping whatever voltage your leisure bank is sitting at into the car battery.

One practical consideration: check your alternator load when the engine's idling versus moving. I found on my setup that pulling 30A through a DC-DC whilst stationary for extended periods was making the alternator work harder than I'd like. The Orion XS's input current limiting helps here — you can dial it back in VictronConnect to something sensible for your specific alternator rating.

Also factor in cable runs and fusing — the XS needs appropriately rated cable both sides, and Victron's own documentation is pretty prescriptive about this.

@CamperShaun that's a useful clarification — so in a pure emergency backup scenario, is there actually much point over just a basic MPPT topped up by a small solar panel?

Genuine question because my setup is primarily for keeping things ticking over when mains fails, not daily cycling. Wondering if the Orion XS is slightly overkill if the car's only ever parked up occasionally rather than being a regular charge source.

Also — does the XS handle LiFePO4 charging profiles properly out of the box, or does it need configuring via VictronConnect first? My Fogstar cells are quite particular about charge voltages and I'd rather not guess.

@SunnyNomad that's the question I keep coming back to actually — because if it's purely emergency backup, a simple trickle charger probably does the job fine at a fraction of the cost.

But where I reckon the Orion XS earns its keep is if the car battery role is more than just "last resort" — like, does it sit in your priority chain at all during low-sun periods? On my static caravan setup I've occasionally wondered whether having a vehicle connection would smooth out those grim January days when the Fogstar bank is getting hammered.

What's the actual discharge scenario you're all trying to protect against? Because that changes whether you need proper DC-DC conversion or just something to keep a starter battery topped off from the main bank rather than the other way round.