FoxESS Community - Owners & Installers Forum

I have a FoxESS EQ4800 L9 battery with 98% SOH, a reported maximum capacity of 41.09 kWh, and a KH10 inverter.

I’m seeing what appears to be an 18.8% energy loss when discharging the battery from 100% down to 20%.

Discharge figures:

• Battery capacity: 41.09 kWh
  Energy remaining at 20% SOC: 8.22 kWh
  Expected energy discharged: 41.09 − 8.22 = 32.87 kWh
  Actual energy delivered: 26.70 kWh
  Energy difference/loss: 32.87 − 26.70 = 6.17 kWh

This means I’m seeing a difference of approximately 6.17 kWh, which is around 18.8% of the expected usable energy.

When charging to 100% auto gain ~4 kWh:

I’ve also noticed something similar when charging.

When charging from 20% SOC (8.22 kWh) to 100% (41.09 kWh), I would expect approximately 32.87 kWh of energy to be required.

However, the system only records around 28.80 kWh of energy used for charging to 100%.

Based on this, I suspect that around 2.2 kWh could be normal charging/discharging efficiency losses, while the remaining ~4 kWh may be related to the BMS, SOC calibration, or potentially a battery fault.

I have already tried discharging the battery down to 10% SOC and then slowly charging it above 80% at around 1–2 kW, but this didn’t resolve the issue.

I’ve been noticing similar figures for the past few weeks.

Has anyone with a FoxESS EQ4800 L9 experienced similar behaviour? Could this be an SOC calibration/BMS issue, or should I be concerned that there is a problem with the battery?

Any advice or suggestions on how to diagnose this would be appreciated.

Thanks!

I have skim read your post, but you may want to check out this large thread here (about 80 posts) viewtopic.php?p=11713#p11713

tl;dr Fox claim that you can discharge to 0% in Australian market, reality is the software (at the time) would only allow 90% to be used (41.93kWh becomes available to use 37.74kWh) so that each 10% drop in SoC isn't 4.19kWh but 3.77kWh (when SoH = 100%)

It was a while ago, but you may have to check the maths.