40 KW Akku nach 3 Stunden leer und zieht noch Strom aus dem Netz beim Entladen

Got a situation with my garden office setup that's doing my head in, hoping someone here has seen this before.

Running a Victron MultiPlus-II 5000 with 4 x Fogstar Drift 200Ah batteries (roughly 16kWh usable) and a Cerbo GX managing everything. The problem is the batteries are draining far quicker than the capacity should allow — I'm seeing them hit low SOC in a fraction of the time I'd expect based on my actual loads.

Worse, even when the system is supposedly discharging, the energy meter is occasionally showing grid draw. Not huge amounts, but it shouldn't be happening at all — I'm set up for ESS with grid tie and the whole point is to stop pulling from the grid during peak rates.

A few things I'm wondering:

• Could the BMS communication between the batteries and the Cerbo be reporting SOC inaccurately, causing the system to think it's lower than it actually is?
• Is it possible one or more batteries have drifted out of balance and the BMS is cutting capacity short to protect cells?
• Anyone had ESS misconfiguration cause phantom grid draw like this?

I've checked the VRM portal and the graphs look a bit odd — the discharge curve drops steeply then almost flatlines before tanking again, which seems suspicious.

Worth noting the MultiPlus-II firmware is recent but I haven't touched the ESS assistant settings since initial setup.

Has anyone dealt with similar behaviour, particularly with lithium packs and Cerbo GX? Would really value some pointers before I start pulling cables.

Mate, "40 KW Akku" in a garden office is either a typo or you've got Jeff Bezos's shed.

@DazHenderson77 😂 yeah I clocked that too — pretty sure OP means 40kWh or possibly just 40Ah, lost something in translation there.

@TransitConvert — without seeing your full setup it's hard to say, but the grid-draw whilst "discharging" screams a MultiPlus config issue to me. Check your ESS assistant settings — specifically the grid setpoint. If it's not zeroed out properly the unit will happily pull from the grid even when the batteries are sitting there ready to go.

Also worth checking your DVCC settings in VictronConnect. Had something similar with my shepherd's hut setup when I first commissioned it — drove me mad for a week before I spotted I'd the charge current limit set wrong.

What firmware version are you running on the MultiPlus?

@TransitConvert the thread title suggests this might have been posted or translated from German — "Akku" is just German for battery, so there's possibly some context missing.

Setting that aside, the symptoms you're describing — battery depleting faster than expected and grid draw during what should be discharge — are classic signs of a few things worth checking:

• SOC calibration in the Victron system. If the MultiPlus-II has incorrect capacity set in VEConfigure, it'll hit the low SOC threshold prematurely and hand off to grid
• Cell imbalance in one of the Drift 200Ah units causing early BMS cutoff
• AC loads exceeding inverter capacity triggering grid assist

Can you pull the VRM data or even a screenshot from the Cerbo/Venus showing the charge/discharge curves? Also confirm how the batteries are wired — parallel or series-parallel — and whether you've got a proper BMS communicating with the MultiPlus via DVCC.

@TransitConvert Regardless of the title oddity, the symptoms you're describing — battery depleting faster than expected and grid draw persisting during discharge — are classic signs of either a misconfigured ESS assistant in the MultiPlus-II or incorrect SOC calibration on your BMS.

With Fogstar Drift cells, if your battery capacity isn't correctly declared in VictronConnect, the system will hit its minimum SOC floor prematurely and start pulling grid to compensate, even though the physical cells still have charge remaining.

Check your DVCC settings and confirm the BMS is actually communicating SOC properly over VE.Can or VE.Bus. Also verify your ESS minimum discharge SOC isn't set too conservatively — sometimes it ships defaulted quite high.

What's your BMS setup — are you running a separate Daly or JK, or relying on the Fogstar's built-in?