Anyone else running a Victron SmartShunt alongside a split charge relay — does the SOC ever settle down?

So I've finally got round to fitting a Victron SmartShunt 500A in the van and I'm genuinely chuffed with how much more visibility I've got into the leisure bank. Running 200Ah of Battle Born LiFePO4 and it's been an eye-opener seeing actual amp draw rather than just guessing.

The issue I'm having is that the SOC percentage seems to drift over a few days of use. I've got a Sterling Power Pro Split r 12v 130A isolator doing the charging from the alternator, and I wonder if the shunt isn't always seeing a proper full charge cycle to reset the 100% threshold. I've set the charged voltage to 13.4v and tail current to 4% in the VictronConnect app, but it still seems to creep down over time even when I know the batteries are full.

Has anyone dialled in their settings specifically for LiFePO4 with a split charge setup rather than a DC-DC charger? I've seen some threads suggesting the charged voltage threshold needs bumping up slightly because the split charge relay drops a bit of voltage before it hits the shunt. Not sure if that's the culprit or whether my peukert exponent is just off — currently left that at 1.05 which I think is roughly right for lithium.

Would really appreciate hearing what settings others have landed on, or whether I'm better off just wiring the sense wire differently.

@Shunt_Guy the SOC drift is real — had the same headache when I first set mine up on the static.

Key thing that sorted it for me: make sure the SmartShunt is the only thing connected directly to the negative busbar. Any other negative paths bypassing the shunt will throw the readings off completely.

Also worth checking your charged voltage, tail current and Peukert settings in the VictronConnect app — the defaults are pretty generic. Once I dialled those in properly for my Fogstar lithiums it settled right down within a couple of charge cycles.

The split charge relay itself shouldn't cause issues as long as all current flows through the shunt. Does your alternator feed run through it or is there a bypass somewhere?

Hey @Shunt_Guy, great setup! One thing worth checking that nobody's mentioned yet — make sure your charged voltage threshold in the SmartShunt settings actually matches what your charger's absorption voltage is set to. If the shunt thinks the battery is fully charged before it genuinely is, the SOC resets too early and compounds the drift over time.

Also with a split charge relay in the mix, are you seeing any brief current spikes when the relay engages while driving? That can confuse the SOC calculation temporarily. Might be worth logging it through VictronConnect to see if that's where the weirdness creeps in.

Battle Born LiFePO4s should behave really well with the SmartShunt once everything's dialled in — lovely flat discharge curve for the SOC to track. Stick with it, it's worth the faff! 🙂

@Shunt_Guy one thing I'd scrutinise is whether all your loads are actually downstream of the shunt — even a single parasitic drain wired incorrectly will corrupt the coulomb counting silently. Easy to miss with a split charge setup where there's often a bit of ad-hoc wiring involved.

Also worth double-checking: what tail current percentage have you configured? On LiFePO4 I found dropping it to around 2-3% of capacity made a significant difference to when the SmartShunt decides it's actually "full." The default 4% felt slightly off on my narrowboat bank.

Have you connected it via Bluetooth to the VictronConnect app to review the charge/discharge history? The synchronisation log will tell you exactly how often it's resetting — that data is quite revealing for diagnosing whether it's a wiring issue or purely a parameter issue.