Discordance de SOC entre le couple BMS Renon/Cerbo GX et un Multi RS

Been noticing something a bit odd on my boat setup and wondering if anyone else has run into this.

I'm running a Renon BMS talking to a Cerbo GX via VE.CAN, with a Multi RS in the mix. The problem is the SOC readings don't agree with each other — the BMS is reporting one figure, the Multi RS is showing something different, and the Cerbo is essentially picking a side rather than consolidating them properly.

From what I can tell, the Multi RS does its own internal SOC calculation based on charge/discharge history, whereas the Renon BMS is reporting cell-level data directly. When they disagree — which seems to happen after a partial cycle or if the battery hasn't hit a proper absorption/float in a while — the Cerbo ends up displaying something that doesn't match either source accurately.

A few things I've tried:

• Setting the DVCC source priority to the BMS
• Forcing a full charge cycle to let everything re-sync
• Checking VE.CAN termination (both ends properly terminated)

The BMS figures feel more trustworthy to me since it's pulling directly from the cells, but I'm not 100% sure the Multi RS is respecting that as the master SOC source.

Anyone running a similar architecture — particularly with VE.CAN rather than VE.Bus — seen this? Is there a Victron setting I'm missing that forces the Multi RS to defer to the BMS entirely, rather than blending or overriding?

Would be good to know if this is a known quirk or something worth raising with Victron support.

@KevScott — classic issue this one. The Multi RS calculates SOC via its own coulomb counter, whilst the Renon BMS is reporting its own SOC over VE.CAN. The Cerbo then has to decide which source to trust, and if it's not configured correctly it'll show a blended or conflicting figure.

In VEConfigure / Venus OS settings, check your "SOC source" under the DVCC menu — you want to explicitly set it to the BMS (Renon) rather than letting it default to the Multi RS's internal counter.

Also worth checking:

• DVCC is fully enabled
• SVS (Shared Voltage Sense) is active
• The Renon is appearing as a "BMS-controlled battery" in the Cerbo device list

The Multi RS coulomb counter drifts unless it gets regular full-charge resets, which is less predictable on a boat with varied charging sources.

@KevScott had the exact same headache in my van build last winter. The Multi RS is stubborn about its own coulomb counter — it doesn't simply defer to the BMS figure even when a proper DVCC setup should, in theory, let the BMS be the authority.

What actually sorted it for me was forcing a full charge cycle to absorption and letting the Multi RS resync from a known 100% point. After that the drift was manageable.

Worth checking your DVCC settings in the Cerbo — specifically that Has DC system isn't ticked if you don't genuinely have one, as that can throw the calculations sideways in confusing ways.

Also check firmware. Victron pushed a fix related to Multi RS SOC reconciliation a while back. Wouldn't surprise me if you're on an older build.

@KevScott worth understanding why the discordance happens before chasing the fix.

The Multi RS uses a standalone coulomb counter that resets its reference point on a full absorption cycle — problem is, it never truly "agrees" with the Renon's cell-level SOC unless you force a proper synchronisation trigger. On my LiFePO4 bank (Fogstar cells, Victron Cerbo), I resolved this by setting ESS Battery monitor explicitly to the BMS source in the Cerbo's system settings rather than letting it default. The Multi RS then defers to that as ground truth.

Also check your VE.CAN termination resistors — a flaky CAN connection causes intermittent dropout where the Multi RS quietly reverts to its own counter mid-session. Took me an embarrassing amount of time to spot that one. Two 120Ω terminators, one at each end of the bus, full stop.

Seen this on my boat too. What sorted it for me was making sure the DVCC settings were properly configured in the Cerbo — specifically setting the BMS as the trusted source. Once DVCC is on and the Renon is feeding cell-level data correctly over VE.CAN, the Multi RS should defer to it rather than going rogue with its own counter.

Worth double-checking your VE.CAN termination as well — a dodgy terminator plug caused me no end of weird data issues before I spotted it.

@TorJake makes a fair point about understanding the root cause first. But honestly for most installs, DVCC config is where I'd start — it's usually the culprit before anything else.

@HappyBuilder +1 on the DVCC point but also worth checking your SVS (shared voltage sense) and SCS (shared current sense) are both enabled under DVCC — not just DVCC itself. Easy to miss.

Had a similar drift on my narrowboat setup with Fogstar Drift cells. BMS was reading 87%, Multi RS thought it was 76%. Turned out my shunt wasn't properly configured as the system shunt in VRM — it was still doing its own thing independently.

Once you designate the correct shunt and let DVCC handle the orchestration properly, the Multi RS should follow rather than freelance with its own counter.