SmartShunt 300A power draw from 12v LiFPo batteries in a mobility scooter

Really interesting topic this — I've been down a similar rabbit hole lately with my static caravan setup and it got me thinking about smaller 12v applications.

I swapped out a tired AGM on a leisure setup last year for a Fogstar Drift 100Ah LiFePO4 and the difference in usable capacity is night and day. But the SOC monitoring side of things is where it gets tricky, isn't it?

From what I understand, a Victron SmartShunt 300A is probably overkill current-wise for a mobility scooter — most of those motors are pulling what, 20-40A peak? — but the Victron kit does talk nicely with their app and gives you proper coulomb counting rather than just voltage-based guesswork. That voltage-based SOC on LiFePO4 is notoriously flat across most of the discharge curve, so a shunt really is the right call if you want accurate readings.

Has anyone here actually fitted a SmartShunt to a smaller mobility or recreational vehicle application? I'm curious whether:

• The quiescent draw of the SmartShunt itself becomes a concern on a small battery that might sit unused for weeks?
• Does the Victron app retain historical data between sessions without a GX device in the loop?

I'm also wondering if the 500A version would be any better or worse suited — I've seen both floating around on Amazon and BatteryMegaStore at fairly similar prices lately.

Would love to hear from anyone who's done this on a compact 12v system rather than a full van or cabin build.

@SueJohnson the SmartShunt draws around 0.9mA idle on 12v which is basically nothing — less than a cheap LED indicator light. On a mobility scooter though I'd be more concerned about the quiescent draw of whatever you're monitoring with it. The Victron app via Bluetooth polls regularly and that adds up if left running.

Bigger gotcha on LiFePO4 at 12v: make sure your shunt is configured for the correct battery chemistry. Out of the box it assumes lead-acid charge curves and your state-of-charge readings will be embarrassingly wrong. Done that myself on the narrowboat before I realised why my "100% full" battery was cutting out two hours later like a sulky teenager.

Set the charged voltage threshold and Peukert exponent properly in VictronConnect and it's genuinely one of the better bits of kit Victron makes. Reasonably priced too, which makes a change.

@Boycie25 that 0.9mA figure is reassuring but I'm curious — does that change meaningfully when it's actively logging or syncing via Bluetooth? I've got a SmartShunt on my van build and I leave Bluetooth enabled permanently, wondering if that's quietly draining more than I think over a week parked up.

Also relevant for @SueJohnson's mobility scooter application — does the SmartShunt actually handle the kind of high-pulse discharge you get from a scooter motor on startup? I know Victron rate it at 300A continuous but peak inrush could be quite different. Has anyone verified it doesn't corrupt the SOC reading after a big current spike?

@StuKnight worth noting the SmartShunt has a "power save" mode in the VE.Direct / Bluetooth settings — when nothing's actively polling it, the BT radio duty-cycles down considerably. In practice on my boat setup I've measured closer to 1.2–1.5mA when the phone app is actively connected and syncing, versus the ~0.9mA at rest.

For a mobility scooter though, the more pressing concern IMO is whether the shunt's being installed across the negative correctly — I've seen a few installs where people accidentally leave a parallel negative path which completely invalidates the current readings. On a small 12v LiFePO4 pack the measurement error would be worse proportionally than on a larger bank.

What capacity is the scooter battery? That might change whether the SmartShunt 300A is even the right size — a 50A or 100A unit might suit better.

@StuKnight to add to what @CliffGazer said — when Bluetooth is actively connected and syncing, draw can spike briefly but we're still talking low single-digit mA at most. On a mobility scooter it's genuinely negligible compared to the self-discharge of even a decent LiFePO4 cell.

What's actually worth watching on a small 12v application like this is the voltage drop across the shunt itself at high currents — the 300A rated shunt is 0.25mΩ, so at sustained high draw you'll lose a tiny bit there. Probably irrelevant on a scooter but worth knowing.

If the scooter sits unused for weeks, I'd be more concerned about the BMS quiescent draw than the SmartShunt. My Fogstar cells have a BMS that pulls noticeably more than 0.9mA in standby.

@CE_Builds that's a useful distinction — so the Bluetooth spike is only during active sync, not just having it enabled but idle?

Asking because on my van setup I leave Bluetooth on permanently so the Victron Connect app can grab data whenever I open it. Wondering if that idle-but-enabled state is meaningfully different from the power save mode @CliffGazer mentioned.

For a mobility scooter with a small LiFePO4 pack the maths matter quite a bit — even a few extra mA continuously across weeks of light use could skew the SOC drift noticeably. Anyone measured the difference between Bluetooth enabled-idle versus power save actually disabled?