Battery drain when using power from grid

Noticed something odd with my setup at the static caravan last week that I wanted to run past folk here.

Running a Victron Multiplus II with a Fogstar Drift LiFePO4 bank. I've got Octopus Agile, so overnight when rates drop through the floor I'd expect the system to pull from the grid and leave the batteries alone — sensible enough in theory.

Problem is, even when grid is actively supplying the loads, the batteries still seem to be cycling slightly. SOC drifting down a percent or two overnight even when there's no real reason for it. Not a massive deal but it bothers me.

My thinking:

• Could be parasitic draw from the BMS or Victron kit itself
• Possibly the Multiplus is pulling a tiny bit from the battery to "stabilise" the AC output
• ESS settings might not be configured quite right for pure grid-preference mode

Worth noting this only seems to happen when the system is in what I'd call "grid priority" behaviour. During the day running off solar it's fine.

Anyone else seen this on a Victron ESS setup? Wondering if there's a minimum discharge current threshold I should be setting, or whether the grid setpoint in VEConfigure needs tweaking.

Happy to share my ESS config screenshots if useful — might be easier than describing it all in text.

@RetiredElectrician the post seems to have cut off mid-sentence but I think I know where you're going with this!

Are you seeing the battery slowly drain even when you're pulling from the grid? On my motorhome setup with a Multiplus II I noticed the same thing — it's usually one of two culprits:

1. PowerAssist kicking in unnecessarily when loads spike
2. The input current limit set too low, so Victron supplements from the battery

Worth checking in VictronConnect what your AC input current limit is set to. Also have a look at whether PowerAssist is enabled — if you don't actually need it, switching it off stops the unit from "helping" with the battery when grid is available.

What's your input limit set to currently? And is this happening at specific times or constantly?

@RetiredElectrician both posts cut off unfortunately — though I reckon I can guess the gist!

If you're on Agile and seeing the battery drain whilst on grid power, the most likely culprit is your AC input current limit set too low in VictronConnect. The Multiplus II will silently pull from the battery to compensate if grid supply is capped below what the loads demand.

Worth checking:

• AC Input Limit in the Multiplus II settings
• Shore power assist is enabled correctly
• Your ESS assistant is configured (if you're running one)

On my own Multiplus II 48/3000, I had something similar when I first set up the ESS assistant — it was "topping up" from the battery during peak loads even with mains connected, which looked exactly like unexplained drain until I dug into the VRM portal logs.

Post your VRM screenshot if you can and we'll crack it!

Both posts cutting off is frustrating — presumably a mobile browser issue @RetiredElectrician.

I'll take a stab at what you're describing: the Multiplus II is drawing from the battery even whilst grid is present? Almost certainly a PowerAssist or ESS configuration issue rather than a fault.

On my cabin setup I had identical behaviour initially. The culprit was the AC input current limit set too low in VEConfigure — the unit was supplementing grid draw from the battery rather than purely passing through.

Worth checking:

• AC1 Input current limit in VEConfigure
• Whether you're running ESS Assistant or plain transfer switch mode
• The Minimum SOC setting if ESS is active

On Agile specifically, if you've got any automated discharge scheduling running via Node-RED or Venus OS, that could also be the cause during certain tariff windows.

Post your VEConfigure screenshots and we can pin it down properly.

Blimey, yes — fat-fingered it on the phone and didn't notice until three people pointed it out, which says something about my proof-reading skills (or lack thereof).

Right, here's the full version: on cheap Agile slots the Multiplus is pulling from the grid as expected, but the Fogstar bank is still showing a slow discharge even when AC In is active. Checked the VRM dashboard and it looks like the PowerAssist threshold might be set too low, so Victron's quietly dipping into the batteries to cover transient loads rather than letting the grid handle it alone.

Anyone tweaked the AC Input Current Limit settings in VE.Configure to stop this? Feels like a wasteful habit when I'm trying to preserve battery cycles for when the rate spikes overnight.

@RetiredElectrician74 Classic Multiplus II behaviour — it's not actually draining the battery, it's the PowerAssist or UPS function keeping the inverter stage warm and nicking a few watts in the process; check your ESS assistant config and set the minimum SOC properly or it'll merrily nibble your Fogstar cells all night convincing itself it's helping.