DESS using Grid during peak hours?

Been wrestling with a similar headache on my boat setup, so this feels timely.

Running a Victron Multiplus II 5000 with a pair of Fogstar Drift 10kWh batteries and 4.8kWc of panels across two SmartSolar MPPT 250/70s. Mostly off-grid but I do have a shoreside hookup for when I'm moored in a marina.

The DESS (Dynamic ESS) scheduling has been brilliant overall, but I've noticed it occasionally pulls from the grid during what I'd consider peak-rate windows — even when the batteries are sitting at 70-80% and solar is actively generating. Genuinely puzzling behaviour.

My theory is that DESS is predicting a high-draw period later in the day and trying to top up "just in case," but the forecasting logic doesn't seem to account for real-time generation properly. The VRM portal shows the decision-making history, but decoding why it made a specific call at a specific moment is still a bit opaque.

A few things I've tried:

• Tightening the minimum SOC buffer settings
• Manually overriding the grid setpoint schedule in certain time windows
• Checking the BMS comms are actually feeding accurate data back to the Cerbo

That last one made a noticeable difference actually — turns out my Cerbo was occasionally losing the BMS handshake which may have caused the Multiplus to assume worse battery state than reality.

Has anyone else dug deep into DESS behaviour with larger battery banks? Curious whether the 16kWh NKON setup mentioned elsewhere in this kind of scenario behaves differently — bigger capacity should give the algorithm more confidence, but does it?

@ForestBoater mate, your Multiplus II is probably ignoring your ESS schedule because the minimum SOC floor is set too low — it'll happily nick grid power the moment it decides the batteries need "protecting" regardless of what time it is.

Check your ESS Assistant settings and bump the minimum SOC up to something sensible during peak hours, or better yet, use scheduled charging in VRM to explicitly block grid input between your peak tariff windows.

With Fogstar Drift cells you've got plenty of usable capacity, so there's no excuse for it to be scavenging expensive units off the grid — mine did exactly this until I stopped trusting the defaults and actually read the manual. Revolutionary concept, apparently.

@RetiredElectrician74 is spot on about the SOC floor, but there's another culprit worth checking — the BatteryLife setting in your ESS config. If it's enabled and Victron's algorithm decides your Fogstar packs aren't getting adequately cycled, it'll temporarily override your schedule and pull from grid regardless of the time window you've set.

In VictronConnect, go into your ESS assistant and check whether BatteryLife is active. On my Multiplus II I actually disabled it entirely once I'd proven the Fogstats were healthy — gives you much tighter control over when grid import actually happens.

Also worth confirming your grid setpoint isn't creeping positive during peak windows; even a modest positive setpoint will bleed grid power in without it being obvious in the logs.

Both @RetiredElectrician74 and @VivaroWanderer are covering the obvious suspects well, so I'll add one that bit me hard last winter: check your ESS scheduled charge windows in VictronConnect — specifically whether "Keep batteries charged" is accidentally ticked for your peak tariff window. Easy to fat-finger on a phone screen.

Also worth verifying your grid setpoint in the ESS assistant. If it's sitting at something daft like +50W rather than a negative value, the Multiplus will happily slurp from the grid to maintain that target even when your batteries are healthy. I had mine doing exactly this for three months before I noticed on VRM. Three months of Octopus peak-rate grief before I spotted it buried in the assistant settings. 😬

VRM's advanced tab shows grid power direction historically — worth a trawl through if you haven't already.

Had exactly this drama with my shepherd's hut setup — turned out my scheduled charges in VRM were set to the right times but the timezone on the GX device was wrong, so Victron was happily hoovering grid at 4pm thinking it was 2am. Check your CCGX/Cerbo clock before you tear your hair out. 🕐

Don't overlook the ESS Assistant input power limit setting — if your grid input current is set too generously, the Multiplus will happily slurp from the meter the moment solar dips below demand, completely ignoring your peak-hour wishes. On my narrowboat I had mine set to 32A and it was treating peak tariff like a free buffet until I throttled it right down during those windows. Pair that with a Node-RED flow on your Cerbo to dynamically adjust the limit by time of day and it'll actually behave itself. 🛶