My Cerbo GX show the batteries discharging

Been scratching my head over something similar with my garden office setup and wondered if anyone else has run into this.

My Cerbo GX is showing negative wattage and current on the battery tile whenever my generator kicks in, even though the voltage is clearly climbing. Visually it looks like the batteries are discharging, but that can't be right if the voltage is rising steadily.

Solar input reads perfectly fine — positive figures, everything looks logical. Switch to the genny and suddenly the numbers flip negative. Wiring hasn't changed, and I've double-checked the SmartShunt connections multiple times.

A few things I'm wondering:

• Could this be a current direction issue with how the shunt is wired relative to the generator input vs the solar MPPT path?
• Is it possible the Cerbo is getting confused about the source and misreporting direction?
• Has anyone needed to adjust any settings in VictronConnect or the Cerbo itself to correct this — maybe something in the system setup around battery monitor configuration?

It's not causing any actual operational problem as far as I can tell — the batteries are clearly charging — but for my emergency backup use case I really want the monitoring to be accurate. If the grid goes down and I'm relying on this system, I need to trust what the screen is telling me.

Running a Multiplus-II alongside Fogstar lithium cells if that's relevant. Would appreciate any pointers from people who've dealt with Victron quirks like this before.

@DaiLewis69 classic one this — almost certainly a shunt orientation issue. The Cerbo's battery tile pulls data from either a BMV-712 or a SmartShunt, and if the shunt was wired with the battery and load sides swapped, it'll invert the current reading permanently.

Check in VRM or the Cerbo console under Device List → SmartShunt → and look at the raw current value. If it's negative at rest or during charge, go into the shunt settings via the VictronConnect app and toggle the "Invert current" option — saves you rewiring.

Had the exact same headache with my garden office Multiplus setup on a Fogstar Drift 100Ah. Took me an embarrassing amount of time to find that one toggle buried in the advanced settings.

Also worth confirming your battery capacity and Peukert exponent are set correctly, as wrong values skew the SOC display wildly.

@DaiLewis69 @DodgyRoamer is spot on about the shunt orientation, but worth adding a bit more detail since you're using a Cerbo GX specifically.

If you're running a Victron SmartShunt or BMV-712, check in VictronConnect that the "Invert battery current" setting matches your physical installation. The shunt has a clearly marked LOAD/CHARGER and BATTERY side — current must flow from battery negative → shunt → load for readings to be correct.

Also double-check your VRM portal settings under Device List → your BMV/SmartShunt → Invert. I've caught this out twice on my narrowboat setup after rewiring.

One extra thing people miss: if you've got a DC-DC charger (Orion etc.) wired between the shunt and battery, that'll throw readings off entirely regardless of orientation. Everything on the load side of the shunt needs to stay on the load side.

Had almost identical grief on my narrowboat last summer — Cerbo convinced me I was haemorrhaging power when actually I was sat on a sunny canal fully charging away like a smug tortoise. 🐢

@DodgyRoamer and @DevonDweller have nailed the shunt angle, so I'll add the bit nobody mentions: once you've flipped the shunt, you also need to go into VictronConnect → BMV settings → scroll down to "Invert current" and toggle that off. Sometimes the software setting survives a physical swap and contradicts itself spectacularly.

Also worth doing a battery state-of-charge sync afterwards — hold the Cerbo at 100% SOC once you've done a proper full charge. Otherwise it'll be reading from a confused baseline and you'll be chasing ghosts for weeks.

@BoxerCamper snap — my narrowboat Cerbo had me convinced I'd somehow invented a perpetual energy drain. Double-check your SmartShunt is wired so current flows into the positive terminal during charging, otherwise Victron's just reading the whole thing backwards like a confused sat-nav. If you've already sorted the orientation and it's still sulking, the battery current calibration offset in the SmartShunt settings via the VictronConnect app can drift — worth a zero-calibration when everything's actually disconnected.