Venus OS 3.81 - BMS Connection lost

Had this exact headache after Venus OS 3.81 landed on my Cerbo GX last Tuesday — BMS connection lost plastered all over the dashboard like I'd done something catastrophic, when really the batteries were sat there absolutely fine.

My setup is a static caravan with a Victron Multiplus-II 48/5000 doing AC coupling duties, and the BMS had been rock solid for months before this update decided to have a wobble.

Few things worth checking if you're in the same boat:

• MK3-USB driver gremlins — 3.81 seems to have upset something in how the Cerbo handles the MK3 interface; try unplugging and replugging the USB after a full reboot, not during
• Check your VRM portal logs — the disconnect timestamps might tell you whether it's dropping periodically or just showing a ghost alarm from the update itself
• Device list refresh — go into Remote Console → Device List and see if the MP2 is actually still communicating properly despite the alarm

Mine cleared after I forced a manual rescan and did a proper power cycle (not just a software restart, an actual DC off, which on a static caravan in November is about as fun as it sounds).

Worth checking the Victron Community forums too — there's already a thread building over there with people on the same 3.81 grief, and Victron's dev responses are usually quicker than you'd expect.

Anyone else on 3.81 with a Cerbo + MK3-USB combo seeing this, or is it just those of us who updated before they'd properly tested the thing? 🙄

Ian1968 | 847 posts | ⚡ Off-grid since 2019

@ForestDaz had almost identical grief after 3.80 dropped actually, so this seems like an ongoing pattern with Venus OS updates and BMS comms. Worth checking your DVCC settings — I found mine had quietly reset to defaults after the update, which knocked my Pylontech stack off completely. Also double-check the CAN-bus baud rate hasn't shifted; 500kbps vs 250kbps catches people out more than you'd think post-update.

Victron's community forum had a thread about 3.81 specifically breaking certain BMS handshakes — might be worth a look over there for your exact BMS brand. What are you running? If it's JK or DALY there are some known workarounds floating about. Rolling back to 3.80 temporarily is straightforward enough if you need the system stable while you troubleshoot properly.

Cleggy | 203 posts | ⚡ Off-grid since 2022

@ForestDaz really sorry to hear you're dealing with this — these unexpected post-update gremlins are the worst! Quick question though: which BMS are you running, and is it connected via USB or VE.Direct? I'm asking because I've got a Fogstar Drift 200Ah and noticed the Cerbo GX can be fussy about which communication protocol it prefers after firmware updates.

Also, did Victron push 3.81 automatically or did you manually trigger it? I've been holding off on auto-updates for exactly this kind of reason — currently sitting on 3.73 and slightly nervous about upgrading now!

Has anyone found a reliable rollback method if needed? Presumably through the Victron Remote Management portal?

LizHunt | 412 posts | ⚡ Off-grid since 2021

@ForestDaz worth checking whether Venus OS 3.81 reset your VE.Can port settings — I had something similar (different BMS, admittedly) where an update quietly changed the CAN-bus profile back to default. Took me ages to spot it buried in the settings menu.

Go to Remote Console → Settings → Services → VE.Can port and confirm the profile matches what your BMS actually expects. Also double-check your DVCC settings haven't shifted — 3.81 seemed to touch a few things it perhaps shouldn't have.

If you're on Bluetooth-connected BMS rather than CAN, the Victron community forum has a thread specifically about 3.81 breaking some BMS reconnection handshakes. Might be worth a browse while you're troubleshooting. What BMS are you actually running?

MuddyNomad | 156 posts | ⚡ Off-grid since 2021

@ForestDaz had this exact drama with my shepherd's hut setup — not on 3.81 but similar behaviour after a previous bump. Worth checking your DVCC settings specifically; a firmware update quietly toggled mine back to defaults and the Fogstar batteries went immediately invisible to the Cerbo. Took me an embarrassing amount of time to spot it.

Go to Settings → DVCC and verify everything matches what you had before. Also double-check the BMS CAN profile under the VE.Can port settings — mine had silently reverted to a generic profile rather than the correct one for my batteries. Two minutes of checking there saved me hours of head-scratching.