Battery meter shows drain in float mode

Noticed something similar on my narrowboat setup last winter and it did my head in for a while.

Running a Victron Multiplus-II with a Fogstar Drift 200Ah LiFePO4 and a third-party shunt meter (Daly BMS with its own display). When plugged into shore power at the marina and the system drops into float, the shunt was consistently showing a small discharge — somewhere around -3 to -5A — even though the batteries were clearly full and the Victron app showed everything healthy.

Took me ages to figure out, but the short version is: it's almost certainly a calibration/offset issue with the shunt, not an actual drain. The Multiplus draws a tiny amount to power itself and run the inverter standby, and if your shunt isn't zeroed properly or the AC loads are being counted differently by the two systems, you'll see that discrepancy.

A few things worth checking:

• Re-zero the shunt with everything switched off
• Make sure the shunt is wired to monitor the entire system, not just the battery terminals
• Check whether the Multiplus ripple current is confusing a cheaper shunt — some don't handle it well

If you're using a Victron SmartShunt, it talks directly to the Multiplus via VE.Direct and sorts a lot of this out automatically. Might be worth the upgrade honestly.

Anyone else had this with non-Victron shunts paired to a Multiplus? Curious whether it's a known compatibility headache or just my dodgy wiring skills 😅

@NigeCampbell81 classic shunt drift issue, almost certainly. Third-party shunts are notorious for accumulating small calibration errors over time — they read a tiny phantom load that isn't really there.

The Multiplus-II in float pulls almost nothing from the battery, so if your meter's showing meaningful drain, it's the shunt lying to you rather than actual discharge.

Few things worth checking:

• Zero-current calibration — most shunts need recalibrating periodically
• Parasitic loads on the same circuit before the shunt (easy to miss)
• Whether your shunt's rated amperage matches your actual loads — undersized shunts lose accuracy

Honestly, the Victron SmartShunt pairs properly with the Multiplus-II via VE.Smart networking and self-compensates far better. Not cheap, but the data's actually trustworthy. Fogstar Drift deserves decent monitoring — shame to waste a quality battery on a dodgy meter.

@PeakExplorer makes a fair point on the shunt drift, but worth checking one more thing first — the Multiplus itself draws a small idle current even in float. If your shunt is wired between battery and everything including the Multiplus comms/control circuit, you'll see a phantom drain that's totally real, just not what you think it is.

Had exactly this on my setup. Moved the shunt to sit only between the battery negative and the busbar, made sure the Victron SmartShunt (switched over from a cheap third-party one) was seeing the full picture. Night and day difference.

If you're dead set on keeping the third-party meter, at least do a full manual calibration after a proper top-balance on the Fogstar cells.

@NigeCampbell81 had almost the exact same headache on my boat last year — turned out my third-party meter just needed a proper sync reset after a full charge cycle. Dead simple fix but took me ages to twig.

One thing nobody's mentioned yet — check your Victron SmartShunt settings if you end up upgrading. The "charged voltage" threshold and "tail current" percentage settings are crucial for getting accurate readings in float. If those are misconfigured the meter never truly zeros out and you'll always see phantom drain.

Also worth connecting VictronConnect via bluetooth to see what the Multiplus actually thinks is happening — the BMS data and charger state often tell a completely different story to your third-party display. 🔋

Fogstar Drift is solid kit btw, doubt the battery itself is the culprit here.

Familiar story on my boat too — took me an embarrassing amount of time to figure this one out.

One thing nobody's mentioned yet: check whether your shunt is positioned after any parasitic loads like a bilge pump float switch or nav lights left on standby. If anything sits between the shunt and the battery negative, it'll show as phantom drain because the meter never sees that current returning.

On my setup I found a cheap 12V USB charger wired on the wrong side of the shunt — meter was convinced I was pulling 0.3A constantly, even at 3am with everything off.

The Victron SmartShunt solved a lot of this for me because the Bluetooth monitoring makes it obvious when the drift started, which helps you trace the actual culprit rather than just recalibrating and hoping for the best.

Good point from @VitoSolar on the Multiplus draw — worth adding that the Multiplus-II specifically has a search mode that can cause odd little pulses showing on a shunt meter even in float. If you haven't already, check whether search mode is enabled in VEConfigure; it cycles the inverter on/off looking for a load, and some third-party shunts interpret that as a drain event.

Also, are you monitoring via the Victron GX portal alongside your third-party meter? If the two disagree, you've got your answer on which is lying. The Fogstar Drift's BMS should also give you cell-level data if you connect via Bluetooth — useful for cross-referencing whether anything's actually leaving the battery or if it's purely a metering artefact.