keep starter and house banks electrically isolated except during charging

Running my static caravan setup with a Victron Orion-TR Smart between a lead-acid starter battery and a Fogstar lithium house bank, and honestly the isolation-except-during-charging approach is the only sane way to live.

The Orion handles it beautifully — set the Li profile at 14.6 V, let it do its one-way magic, and your starter battery isn't getting dragged down by whatever nonsense the leisure side gets up to overnight. 🔋

What I'm curious about though — for those of you doing similar setups on cabins or caravans — are you running the Orion in standalone mode or are you triggering it via the ignition line? I've been going back and forth on this because:

• Standalone means it charges whenever the input voltage looks healthy enough
• Ignition-triggered is cleaner but adds a wire run that's annoying in a static install

Also, has anyone had issues with the Orion not recognising that the alternator is actually running, especially on newer vehicles with smart alternators doing that variable-voltage trick? I've read horror stories about the unit thinking 12.8 V means "charging" when it's just resting voltage.

The isolation bit feels like the killer feature nobody talks about enough — your lithium house bank genuinely cannot murder your starter battery if the DC-DC is your only bridge between them. No VSR nonsense, no accidental parallelisation during a flat-battery panic moment.

Anyone else gone full Orion-TR Smart for this, or are you using something like the Sterling B2B instead? Genuinely interested in what's working out in the real world for UK off-gridders.

@VanKen yes, that's the correct approach and frankly non-negotiable with mixed chemistries. Lead-acid and lithium have fundamentally different charge profiles — you cannot let them sit in parallel passively. The Orion-TR Smart handles this properly because it's doing genuine DC-DC conversion, not just closing a relay.

Worth noting: in my shepherd's hut setup I've got the Orion configured with the ignition sense wire so it only activates when the alternator is actually charging, not just when the vehicle is "on." Subtle but important distinction — avoids discharging your starter battery into the house bank when you're sat stationary with the engine off.

Also set your input voltage cutoff conservatively. I run mine at 12.8V minimum input to protect the starter battery from being dragged down.

What input/output current rating did you spec?

@VanKen the Orion-TR Smart handles this beautifully in isolated mode — worth double-checking your input/output voltage thresholds in the VictronConnect app though. By default it'll start charging at 13.2V and disengage around 12.8V, which on a tired lead-acid starter can cause it to cycle erratically.

I run a near-identical setup in my motorhome; bumped my start threshold to 13.4V and haven't had issues since. Also worth enabling the engine shutdown detection delay if you're on a vehicle — prevents the Orion draining your starter trying to top the lithium right as you kill the ignition.

The isolation @SomersetVanLifer mentions matters most during discharge — never want that lithium BMS cutting out and leaving your lead-acid holding the load solo unexpectedly.

@VanKen one thing worth adding to what @SomersetVanLifer and @ExFirefighter42 have mentioned — make sure you've got the Orion-TR Smart set up with a proper engine-running detection method if you're in a static setup without a traditional alternator signal. Some folks use a voltage threshold trigger, but with lead-acid resting voltages being a bit unpredictable, you can sometimes get false triggers. A dedicated ignition sense wire is cleaner if you have that option. Also worth keeping an eye on the Victron Connect app periodically — the charge history logs are genuinely useful for spotting if anything odd is happening between the two banks. Lovely bit of kit overall though, runs our setup without a fuss.

Yeah @VanKen solid setup. One thing nobody's mentioned yet — make sure your Orion-TR Smart is configured in standalone mode if you haven't got a VE.Direct connection running to a Cerbo or similar. Without that, it relies purely on input voltage thresholds to detect engine-on/off, which can occasionally misfire on a static caravan where your input voltage sits in that awkward middle range.

Worth setting the engine-detect threshold manually in the VictronConnect app rather than leaving it on defaults.

Also — fuse both sides of the Orion, not just the input. Seen people skip the output fuse because the Fogstar BMS "handles it." It doesn't handle a short between the Orion and the battery terminals.

Running a similar split on my garden office setup, same principle applies even without an alternator in the mix.