Orion XS Bulk restart voltage question

Got a bit confused with the Orion XS settings in Victron Connect and hoping someone can clarify.

Running it in my shepherd's hut to charge a 12V lithium bank (Fogstar Drift 100Ah) from the vehicle alternator. I've been tweaking the bulk restart voltage offset and noticed the app displays a calculated restart voltage — looks like it's working off the float/storage voltage minus whatever offset you dial in.

What I'm not 100% sure about is which voltage it actually references when calculating that threshold. Is it always pegged to the float voltage, or does it switch to storage voltage if you've got storage mode enabled? The two are obviously different values so it matters quite a bit in practice.

Also — does the restart trigger off the battery voltage or the input side? I'd assumed battery but now I'm second-guessing myself after reading the manual three times and still feeling none the wiser. 😅

My current offset is set to 0.4V but honestly I'm not confident that's sensible for LiFePO4. Anyone running a similar setup with the XS who's found settings that work well in the real world rather than just on paper?

@BigAl27 the bulk restart voltage is basically the threshold where the Orion XS decides your battery needs charging again after it's already done a full cycle.

For lithium (especially Fogstar Drift) you want it set fairly low — something like 13.0V otherwise it'll kick in constantly and annoy you. Had mine set too high on the boat initially and it was cycling every 20 mins, drove me mad 🙄

The Drift BMS is pretty robust but no point hammering it unnecessarily.

Key thing people miss — this setting works alongside your charger enable input if you're using one. Worth checking the Fogstar docs for their recommended float voltage too and working backwards from there.

What alternator are you running it off? Makes a difference to how aggressive you want those settings.

@BayLisa has covered the basic concept well. Worth adding — with Fogstar Drift cells specifically, I'd set the restart a fair bit below your absorption voltage, otherwise the Orion keeps kicking back in unnecessarily once the BMS does its thing.

On my van setup I run the restart around 12.9V for a similar lithium bank. Seems to hit the sweet spot without the unit cycling on and off constantly.

Also worth double-checking your absorption and float voltages match what Fogstar actually recommend — their Drift cells are slightly particular about charge parameters. The defaults in Victron Connect aren't always spot on for every lithium chemistry.

@WonkyMender's Fogstar-specific point is key — those Drift cells have a relatively flat discharge curve so don't be fooled by the resting voltage sitting deceptively high for ages before it actually needs a top-up. I'd lean toward ~12.8V restart personally; anything lower and you're basically waiting until the battery's already grumpy before the Orion XS bothers waking up. Worth noting the Orion XS also needs the input (alternator) voltage to be healthy before it'll trigger anyway, so if your vehicle's at idle with a lazy alternator, the restart threshold becomes almost academic — seen that catch people out in my motorhome setup more than once.

One thing worth flagging that nobody's mentioned yet — make sure you're accounting for voltage drop along your cable run between the vehicle and the hut. If your cables are on the longer side or a bit underspec'd, the Orion XS could be seeing a slightly inflated voltage at its input terminals compared to what the alternator's actually delivering. This can occasionally cause it to think charging is complete when it isn't quite. Not a bulk restart voltage setting as such, but it can affect how the whole charge cycle behaves in practice. Worth measuring actual voltage at both ends when it's running to get a proper picture before you finalise your settings. @FormerCop's point about the flat discharge curve is dead right too — catches a lot of people out with lithium.