Non-optimal DESS performance

Has anyone else been noticing their DESS not behaving optimally during peak tariff windows? I'm running a Victron-based setup and monitoring a couple of systems for friends and family, and I keep seeing moments where the battery should be discharging at full capacity — say during the evening peak on Agile — but it's throttling back for no obvious reason.

A few questions I'm trying to work through:

• Is it the BMS communicating a lower discharge limit than the actual usable capacity? My Fogstar Drift cells seem fine when I manually push them harder
• Could it be the ESS algorithm being overly conservative about the SOC buffer?
• Or is it something in how DESS is calculating the forecast vs actual grid price spikes?

I've been digging through the Venus OS logs but it's not immediately obvious what's causing the hesitation. Wondering if it's a firmware version thing — I'm on a fairly recent build but not the absolute latest.

Anyone monitoring multiple systems seeing the same pattern across different battery brands? Curious whether it's consistent across, say, Pylontech vs DIY lithium setups, or whether it points to something more specific in the algorithm.

Would love to know if there's a parameter worth tweaking in the DESS settings, or whether this is something Victron need to address on their end. Has anyone raised it with them directly?

@Cleggy what's your SOC target set to when DESS kicks in? I ask because on my static caravan setup I had a similar thing — the system kept discharging into what should've been a hold window. Turned out my scheduled charge slots in VRM weren't aligned properly with my Octopus Agile peak periods. Shifted everything by 30 minutes to account for the BMS balancing overhead and it sorted itself out almost immediately.

Also worth checking — are your ESS mode settings actually pushing to the MPPT or just the inverter? Caught that catching me out with my Fogstar batteries last winter.

What firmware are you on? There were some known DESS quirks on older Venus OS builds that caused exactly this sort of behaviour.

@Cleggy DESS performance issues during peak windows are almost always down to one of three culprits in my experience:

1. Incorrect battery capacity figure in VenusOS — if your usable capacity is understated, DESS gets conservative and won't discharge as aggressively as you'd expect
2. BMS communication lag — if you're running Fogstar Drift or similar with a CAN/DVCC setup, occasionally the reported SOC lags behind reality and DESS backs off unnecessarily
3. Grid setpoint misconfiguration — worth double-checking your minimum SOC during peak discharge is actually lower than your target

On my narrowboat I found DESS was also being confused by inconsistent AC loads. The algorithm needs reasonable load history to predict correctly, so erratic consumption patterns genuinely throw it off.

What firmware version are you running on the Cerbo/CCGX? There were some notable DESS improvements in recent VenusOS releases worth checking against.

@Cleggy interesting one this. I'd add something nobody's mentioned yet — BMS communication latency.

On my motorhome setup I run Fogstar Drift cells with a JK BMS, and I noticed DESS was making decisions based on slightly stale SOC data. The Victron CCGX was polling the BMS just slowly enough that during rapid load changes in a peak window, it was essentially flying blind for a few seconds.

Fixed it by switching to a Cerbo GX with proper VE.Direct comms — the difference was immediate. DESS actually trusted its own SOC readings and stopped doing that weird hesitation thing before committing to discharge.

Worth checking your DVCC settings too. If cell-level voltage limits aren't being respected properly through DVCC, DESS will back off unnecessarily when it thinks it's hitting limits that it isn't really hitting.

Great thread. One thing I'd throw into the mix that nobody's touched on yet — have you checked your grid setpoint configuration in VRM? I've seen DESS seemingly "miss" peak windows not because of any BMS or SOC issue, but because the ESS assistant was fighting against an incorrectly tuned grid setpoint, causing it to bleed energy back into the grid rather than hold reserve for the peak window discharge.

@DevonDweller makes solid points as ever, and @LiFePO4Nerd's BMS latency angle is worth investigating too, but I'd rule out the grid setpoint first as it's a quick check. In VRM go to the ESS settings and confirm your minimum SOC and grid setpoint aren't working against each other. Sometimes after a firmware update these can drift from where you'd set them. Has anything updated recently on your Cerbo, @Cleggy?