FoxESS Community - Owners & Installers Forum

Hello,
I have a FoxESS hybrid system with an EP5 battery and a KH7.5 inverter configured in backup mode. Every day, at almost the same time early in the morning, the battery discharges by about 5% (from 97% down to ~92%), even though:

There is no load connected to the backup output,

The system shows no faults,

The inverter remains in normal operation,

Grid power is stable.


After that drop, the battery stays at ~92% until solar production starts.

My question is:
Is this daily scheduled discharge normal behavior for the EP5/BMS or for FoxESS hybrid inverters?
If so, what internal process causes this (e.g., cell balancing, BMS calibration, internal maintenance cycle)?
And is ~8% a typical amount?

I have attached some images to illustrate this behavior.

I would appreciate any clarification or documentation explaining this behavior.
Thank you!

Remember running the batteries and the bms uses power so you will have a slow drain on the batteries with is normal even with no load.

Thank you for the reply.
I'm expecting and seeing an slow discharge on the battery. The behavior that I don't get is the sudden and relatively fast discharge that happens every day at around 06:00 AM till 07:00 AM. That looks quite different from what I expected.

That is a charge event not a discharge event

Thank you for your quick reply. Maybe I'm missing something here and I do feel rather dumb, but I still don't get what happens during that time. I see a constant battery drain and than indedd at the end of it a quick charge. But I still don't understand why am I seeing that discharge in the first place. And it's only on the morning (per first picture). Why not during the whole day or no discharge at all?

Honestly, I still can't understand the reason for that drain in a battery that's acting as an unused backup.

Hi,

Just to be clear, that big spike is *charging* not discharging.
The discharge is indeed happening but very slowly over a long period of time. I guess the sudden charge happens when the SoC dips within the threshold where the inverter decides to charge again.

As for the constant discharge, not sure if that's normal or not. Batteries do all have a small self-discharge rate, and any BMS circuitry as Will mentioned will have a draw too, so I would expect some. How much depends on the system design itself.

- Ret