Anyone else running Victron MPPT + Cerbo GX without a BMV shunt — worth adding one?

Got a 200Ah Fogstar Drift LiFePO4 in the motorhome paired with a Victron SmartSolar 100/20 and a Cerbo GX. Everything talks via VE.Direct and the app looks brilliant — but I've noticed the state of charge figure drifts a fair bit after a few cloudy days of partial charging.

The Cerbo can estimate SoC from the MPPT data alone but it's basically guesswork without a proper shunt in the loop. Tempted to add a Victron SmartShunt 500A so the battery monitor is actually counting coulombs rather than inferring from voltage curves.

Main question: has anyone added a SmartShunt to an existing Cerbo setup and noticed a real-world improvement in SoC accuracy? Particularly curious whether it helps when you're running loads overnight and only getting 60–70% back in during a dull Dorset winter day ☁️

Also wondering if the VE.Smart Networking between the SmartShunt and MPPT adds anything meaningful on top of what the Cerbo already does — or is that overkill at this point?

LiamWalker | 847 posts

@DorsetExplorer — yes, absolutely worth it. The MPPT's SoC estimate is solar-input-only, so the moment you're running loads without charging, it loses track pretty sharpish. A BMV-712 (or SmartShunt if you don't need the physical display) gives the Cerbo a proper current measurement from all sources and loads, which transforms the accuracy completely.

With LiFePO4 the flat voltage curve makes voltage-based SoC essentially useless anyway — you really need coulomb counting from a dedicated shunt. Once it's wired in and connected via VE.Direct, the Cerbo pulls everything together beautifully and the dashboard actually makes sense.

The SmartShunt is the tidier install in a motorhome if space is tight. Roughly £80–90 and genuinely one of the best upgrades I made to my setup.

WendyFisher61 | 312 posts

Had the exact same question when I set up my narrowboat last spring. The Cerbo does a reasonable job piecing things together, but without a shunt it's essentially guessing at what's leaving the battery — it only sees the solar side.

Added a BMV-712 to my 200Ah Fogstar setup and the difference in accuracy was immediately obvious. Coulomb counting is the only reliable way to track net in/out, especially when you've got a 12V compressor fridge, shore power and solar all doing their thing simultaneously.

On the motorhome I ran shunt-less for about six months and kept getting caught out with lower SoC than the app suggested. The BMV-712 paid for itself the first time it stopped me flattening the cells on a cold overnight.

It's not an optional extra in my view — it's the missing piece.

ShedGenius | 1,203 posts

@DorsetExplorer the bit people miss is that the Cerbo can do SoC synthesis without a shunt, but it's basically educated guesswork — it doesn't see your 12V loads at all, only what the MPPT is pushing in.

On my narrowboat I ran without a BMV-712 for about six months and the dashboard read 94% whilst my lights were visibly dimming. Added the shunt, suddenly the whole picture made sense.

BMV-712 Smart is the obvious choice — integrates natively into VRM, zero faffing. The SmartShunt 500A is slightly cheaper if you don't need the physical display.

With a Fogstar Drift specifically, accurate SoC matters more than with AGM because LiFePO4 voltage curves are so flat — voltage alone tells you almost nothing.