Chargin Starterbattery (24V) while Engine is off (Camping) from a 12V LiFePO Powerbank: OrionTrSmart

Been down this exact rabbit hole on my boat — running a 12V LiFePO4 bank and wanting to top up a 24V starter battery while we're moored up, and the Victron Orion-TR Smart docs had me reading the same sentence four times wondering if I'd gone daft.

The Orion-TR Smart 12/24-15 is indeed designed to step voltage up (12V in → 24V out), but every Victron diagram, every YouTube walkthrough, and apparently the bloke at my local chandlery all assume you're going the other direction — alternator charging your leisure bank while underway.

So the question I'm putting to the forum: has anyone actually run one "backwards" from a 12V LiFePO4 powerbank to maintain a 24V starter? Technically the converter should handle it, but I'm a bit wary about:

• Whether the BMS on the LiFePO4 side plays nicely when the Orion wakes up and starts drawing
• Keeping the starter battery healthy without accidentally deep-cycling it (Fogstar cells don't grow on trees, as my wallet knows)
• Whether you'd bother with a DC-DC at all or just use a trickle charger off an inverter like a caveman

I've got a Victron SmartShunt on the 12V bank so I can at least keep an eye on what's being pinched, but I haven't wired it up yet because something feels off about my logic and I'd rather ask first than have a crispy bilge later.

Anyone done this? What am I missing?

@VickyWard the Orion-TR Smart is strictly a buck converter — it steps down, so 12V → 24V simply isn't possible with that unit, full stop. You'd need the non-isolated Orion-TR in the correct ratio, but even then 12V input can't produce 24V output.

What you actually want is a boost converter — something like a Victron Orion-TR 12/24-10A (isolated version) which can genuinely step up. Double-check the isolated vs non-isolated distinction carefully in the datasheet because the product naming is genuinely confusing.

Worth noting: LiFePO4 banks sitting at rest voltage under 13V might not give the Orion enough headroom to regulate cleanly, so factor in your state-of-charge before relying on this for reliable top-ups at the marina.

@PanelEwan is right that the standard Orion-TR Smart won't do it, but worth clarifying for anyone stumbling on this thread — Victron do make isolated Orion-TR Smart units that can step up as well as down, but even those top out at specific input/output combos. Worth checking the exact model number carefully.

That said, for my emergency backup setup I've ended up just keeping a small dedicated 24V trickle charger connected to shore power when moored. Simpler and no converter inefficiency eating into your LiFePO4 capacity.

Has anyone actually used a third-party DC-DC boost converter for this? Wondering whether something like a Renogy unit could handle the job reliably, or whether it's just not worth the hassle compared to a proper mains solution when you've got shore power available anyway.

@VickyWard @SunnyNomad makes a good point worth expanding on — if you do need 12V to 24V, you're looking at a proper boost converter or an isolated DC-DC charger that supports that voltage ratio. Victron don't make one for that specific use case as far as I know, but there are alternatives worth researching. That said, it's worth stepping back and asking why your 24V starter battery needs topping up while moored — if it's regularly going flat without the engine running, that might be a separate issue worth addressing at the source rather than adding complexity to compensate. What's actually draining it? Might be a simpler fix than wiring in another converter. 🙂

@WheresMeWires16 has covered the boost converter angle well. One practical thing worth adding from my own boat setup — if you're regularly moored up and needing to maintain a 24V starter battery, it might be worth questioning whether a DC-DC converter is the right tool at all.

A small dedicated 24V trickle charger running off your 230V inverter (assuming you've got shore power or a decent inverter) is often cleaner and simpler than chaining converters together. Victron's Blue Smart IP65 24V charger is tidy and not expensive.

If you're genuinely off-grid with no inverter option, a standalone boost converter can work but efficiency losses stacking 12→24V mean you're burning more of your LiFePO4 bank than you'd expect. Worth running the numbers before committing to any hardware.