FoxESS Community - Owners & Installers Forum

I am confused regarding temperatures and charging rates.
System
H1-3.7-E
4 of Mira HV25 (10kW)

I am having trouble with my system with low charging rates and know this is temperature related. I have looked elsewhere on this forum and it says slow charging is related to battery temperature.
However in my system it seems more related to inverter temperature. I attach screen shot from the web page and the battery temperature is fairly constant (15 to16) (except today when 10 ish) whereas inverter temperature increases markedly and so does charging.
I have just looked (09/02/25 12:00) on the app and it shows battery temp as 4.5, whereas the web shows battery temp as 10.6.
On 30/12/24 Battery (web)went from 16.5 at start to 16.7 as charging increases whereas inverter went from 16.8 to 23.
On 29/12/21 Battery (web) went from 15.8 to 16.2 whereas inverter went from 16.8 to 23.
The battery temperature (web) was higher on 30th at start (16.5) than the point at which the charge increased on 29th (16.2)
The common seems to be inverter temperature which appears to need to be above 23 ish.

Comments please.

The values reported for battery temperature in the cloud is actually the bms which can be 10-12 warmer than the battery cells.
If you open the Fox v2 app up on your mobile and go to device > battery you should be seeing the cell temp.

The inverter temperature has nothing to do with battery charge speed, it's all about that the bms thinks the coldest cell temp is.
The inverter wants to be a cool as possible as this will increase it's life span but the batteries want to live between 20-25c for best performance. Under 10-15c you'll see serious current limits kicking in.

Yes, my HV25s reduce to around 0.55kW charge rate per battery below 10C min cell temp (about 10A). With 6 batteries I get about 3.3kW charge rate. For you, with four, I'd expect about 2.0-2.2kW below 10C (as your trace shows). This will drop further if below 5C until no charging occurs at 0C.

As Will mentions above, you need to go by the temperature shown in the v2.0 app. The value in the cloud will always be much higher.

I, too, was searching for answers about this topic yesterday. I was wondering why the battery was charging slowly in hours of sunlight (while exporting unused power to the grid!) compared to January 3rd when the battery reached 100% in a few hours. Using the data download facility from the Fox v2 app, I examined my system's January data to date. It appears the charge current (MaxChargeCurrent) switches at particular (CellTempLow) temperatures: 2A at 5.9°C and below; 5.5A for 6.0°C to 10.9°C; and 10A from 11°C. Not sure if this is officially documented anywhere.

It seems a number of people insulate the batteries and some even install moderate heating to keep the batteries at optimum operating temperature of 15-25°C

Examine your own data as your system may differ.

AstroJohn wrote: Fri Jan 10, 2025 8:51 pm ...
It appears the charge current (MaxChargeCurrent) switches at particular (CellTempLow) temperatures: 2A at 5.9°C and below; 5.5A for 6.0°C to 10.9°C; and 10A from 11°C.
...

Very interesting, thank you. Which battery is that for? (& if on a stackable system, how many modules?)

We have a single EP5 battery