XS1400 in promaster van with 24v system

Has anyone else had issues with a Victron Cerbo GX misreading battery state on a 24v lithium setup?

Running a fairly standard van build — 24v system with Fogstar Drift 200Ah cells, Victron MPPT, and a Victron Multiplus-II 24/3000. The Cerbo is showing the battery bank as discharging even when solar input is clearly exceeding load demand. The numbers just don't add up.

I've been back and forth with the supplier and done the usual — checked all the configuration settings in VRM, confirmed the battery voltage parameters are set correctly for 24v, updated firmware on the Cerbo. Everything looks right on paper but the GX seems to be interpreting the voltage readings incorrectly somehow. Almost like it's getting confused between charge and discharge states when the voltage sits in a certain midrange band.

A few things I'm wondering:

• Is this a known issue with the Cerbo when paired with certain 24v lithium chemistries?
• Could the charge curve settings in the MPPT profile be throwing off what the Cerbo reports?
• Has anyone resolved this by adding a SmartShunt to give the Cerbo a proper current-based SOC reading rather than relying on voltage alone?

Currently the Cerbo is just pulling data over VE.Direct from the MPPT — no dedicated battery monitor in the system. Wondering if that's the root cause and a SmartShunt would sort it.

Would really appreciate hearing from anyone who's hit similar weirdness on a 24v build. Doesn't seem to be a 12v issue from what I can find searching the forums.

@Nessa73 classic Victron behaviour — the Cerbo GX thinks it knows your battery better than your battery does. Bit like a sat nav confidently telling you to turn into a lake.

Few things worth checking:

• Battery monitor settings — make sure you've input the correct capacity and Peukert exponent for your Fogstar cells

@Nessa73 worth checking whether you've actually configured a proper battery profile in the Cerbo — it defaults to lead-acid parameters which are completely wrong for lithium. The absorption/float voltage thresholds will throw the SOC reading off entirely.

On my boat setup I had similar grief until I went into the VRM portal and manually set the charge voltages to match the Fogstar spec sheet. Also make sure your battery monitor is set to the correct capacity — Victron's SOC calculation is coulomb-counting based, so if the reference point is wrong everything downstream is wrong.

One other thing: are you using a Victron BMV-712 or relying solely on the Cerbo's internal monitoring? The latter is considerably less accurate without a dedicated shunt in the circuit. Would make a significant difference to the readings you're seeing.

@Nessa73 had similar grief with my Cerbo on a 24v build. Turned out my issue was the battery monitor hadn't been set as the primary source — Cerbo was ignoring the Victron BMV and just estimating from voltage curves instead. Dead wrong with lithium obviously.

Worth checking under Settings > System Setup > Battery Monitor and making sure it's pointing at your actual shunt/BMV rather than "Automatic". Made a massive difference here.

Also — are you using a Victron SmartShunt or something else? If it's not native Victron kit talking over VE.Direct the Cerbo can be a bit funny about trusting the data.

Really interesting thread — had a similar head-scratch on my van build, though I was running 12v rather than 24v.

@LuckySkipper's point about the battery monitor selection is probably the key one here, but I'm curious — are you using a Victron BMV or the SmartShunt alongside the Cerbo, or relying purely on the MPPT data for your state of charge readings?

On my setup the Cerbo was wildly optimistic until I told it explicitly which device was the "source of truth" for battery monitoring. The Fogstar Drift cells are brilliant but the Cerbo won't magically know their characteristics without a proper custom profile set up.

Have you tried connecting via VRM portal to see what the Cerbo is actually logging historically? Sometimes the pattern of misreadings tells you exactly where the config has gone wrong.

Hey @Nessa73, one thing worth checking that hasn't been mentioned yet — make sure your Cerbo is actually receiving data from the correct source for State of Charge. If you've got both an MPPT and a separate battery monitor connected, the Cerbo can sometimes prioritise the wrong one and give you a confused SoC reading. Head into Settings > System Setup > Battery Monitor and confirm it's pointing at the right device. Also, with Fogstar Drift cells specifically, double-check your battery capacity figure is entered correctly in the monitor settings — even a small discrepancy there can throw the percentage readings off noticeably on a 24v system. Sounds simple but it catches people out more often than you'd think!