Anyone else running a split-charge relay alongside a B2B charger — or is it overkill?

So I've been scratching my head over this for a few weeks now. I've got a 200Ah lithium leisure battery in my Transit-based camper and I'm using a Victron Orion-Tr Smart 30A B2B to charge it from the alternator while driving. Works a treat — but someone at a meet-up last month told me they still run a split-charge relay as well, as a backup for when the B2B supposedly "can't keep up."

Thing is, I can't quite see the logic. The Orion is already doing intelligent DC-to-DC conversion and protecting the van's alternator from the lithium's hungry bulk charge demands. Chucking a relay in parallel feels like it'd just defeat the whole point — you'd be hammering the alternator directly again, surely?

For context, I do mostly weekend trips with the odd week-long jaunt in summer. The 30A Orion typically gets me from 20% back to around 80% over a 3–4 hour motorway run, which I'm pretty happy with. I've not felt like I'm missing anything, but now I've got the doubt planted in my head.

Has anyone actually tested running both simultaneously, or is this one of those "it made sense in the AGM days" habits that's followed people into the lithium era?

@CamperAndrea — pull the split-charge relay out and don't look back.

Ran exactly this combo on my old Ducato for about six months, thinking the relay gave me a useful "backup path." All it actually did was dump unregulated alternator voltage straight onto the lithium when the Orion occasionally had a strop during a firmware update gone wrong. Nearly cooked the cells.

The Orion-Tr Smart is your charger. That's the whole point of it — controlled, profiled DC-DC charging that protects both your alternator and your lithium. A split-charge relay alongside it isn't redundancy, it's interference.

Your Transit's smart alternator will thank you too. Those variable-voltage systems absolutely hate having a raw relay-connected lithium battery acting like a black hole on the circuit.

One job, one tool. Sell the relay.

Hey @CamperAndrea, I'd lean the same way as @ExmoorCamper on this one. The Orion-Tr Smart is already doing the heavy lifting — it's managing voltage, current limiting, and protecting your alternator from the lithium battery's hungry initial draw. That's precisely what a B2B is for.

Stacking a split-charge relay on top doesn't really add anything useful, and could actually create a bit of a headache depending on how they interact with each other during the charge cycle.

If you're worried about redundancy, your energy is better spent fitting a proper battery monitor so you can actually see what's happening. Victron's BMV-712 pairs nicely with the Orion ecosystem.

Keep it clean and simple — fewer components means fewer potential failure points when you're miles from anywhere. 👍

@CamperAndrea curious what made you want to keep the split-charge relay in the loop — is it a fallback thing in case the Orion-Tr develops a fault, or more of a "belt and braces" mindset?

I'm running a similar setup and I keep wondering whether there's any scenario where having both actually causes problems rather than solving them. Like, could the relay dump unregulated alternator voltage into a lithium bank if something fails in a weird sequence?

Has anyone actually measured what happens at the battery terminals when both are active simultaneously? Would love to see some real voltage logs rather than just theory. The Victron app should show that pretty clearly if you've got it paired up.

Great question from @Cleggy actually — worth addressing that directly before deciding.

@CamperAndrea the one scenario where keeping the relay might make sense is if you've got 12V accessories drawing directly from the alternator feed that need isolating from your leisure bank regardless of the B2B. But for pure charging purposes? The Orion-Tr Smart handles that elegantly on its own, and you're actually protecting your alternator better without the relay dumping straight onto a hungry lithium.

One thing worth checking — does your Transit have a smart alternator with variable voltage? If so, the B2B isn't just convenient, it's genuinely essential for getting a proper charge into lithium. The relay would likely struggle to see adequate voltage half the time anyway on those newer engines.

Simplify where you can is my general advice. Less to fault-find on a rainy campsite in Wales!

Split-charge relay alongside a B2B is like wearing both a belt and braces — then also stapling your trousers to your shirt, just in case.

The Orion-Tr Smart already handles the protection side properly; a relay dumping unregulated alternator voltage straight onto lithium cells is exactly the sort of thing that'll have you replacing a Fogstar battery far sooner than you'd like.

That said, @CamperAndrea — if your relay is wired to a completely separate load circuit (not the leisure battery directly), then fine, it's not actively doing harm. But if it's paralleling the B2B output onto the same battery terminals, pull it out. It's not a fallback, it's a liability.

Static caravan dweller here, not a camper man, but I've seen enough botched van wiring on this forum to know "belt and braces" usually just means twice as many things to go wrong.