EQ4800-L9 capacity mismatch: 41.9 kWh capacity but measured ~37 kWh

[StarryTissue]

I have a Fox ESS EQ 4800-L9 stack that is listed as 41.9 kWh of storage. I’ve been discharging it for 2 hours each night at the max rate. Both Home Assistant logs and the Fox cloud export show a steady discharge power of 14.7 kW.

• Battery starts at ~100%
• After 1 hour is at ~60% (drop of 40%) | Picture below from home assistant readings
• After 2 hours is at ~20% (drop of another 40%)
• Logs from Home assistant and Fox show discharge rate of 14.7kw. That should equate to 35% battery discharge (14.7 / 41.9)

System details

• Battery: Fox ESS EQ 4800-L9 stack (stated 41.9 kWh)
• Inverter: H4-15.0- Smart
• Master firmware: 1.36
• Slave firmware: 1.0

I have tried charging and discharging battery to 100% but the results are the same. Is there an issue with the battery management software or any other reasons I seem to be missin about 10% of the stated battery capacity.

I have also seen the same results on a friends set up with the same inverter and battery stack.

[MaterialBarracuda48]

For those in the UK, here is the image

OP: https://help.imgur.com/hc/en-us/article ... ed-Kingdom
So best attach images directly to the forum

[StarryTissue]

For those in the UK, here is the image
gWKe8LKl.jpg

OP: https://help.imgur.com/hc/en-us/article ... ed-Kingdom
So best attach images directly to the forum

Thanks and apologies. Will do in the future.

[MaterialBarracuda48]

Thanks and apologies. Will do in the future.

It's ok, you wouldn't know that it is blocked.

Hopefully you get an answer to your post shortly.

From my limited understanding of these, they are a stack of 9... 1 master and 8 slave units. Total capacity is 41.93kWh with a full 100% DoD.

Is your system reserving 10% capacity, so blocking off around 4.2kWh?

[Dave Foster]

It's quite a linear fall so no obvious jumps, but it is a significant sustained discharge power, how much power does it take to recharge the battery to 100%, is it consistent?, what power does your 'rpower' sensor show for the same period.

On V1 batteries when they were deep discharged, they used to benefit from the battery max charge power being reduced to 5A when the SoC gets to 94%, a lot of balancing occurs here and the lower DC power gives the pack more time to balance.

[StarryTissue]

I will do a controlled test: Force Charge to 100% followed by a deep discharge and share the graphs today.

In Home Assistant, can you know which stat you would like to see so I share the right info?

Any of these?

[MaterialBarracuda48]

I have a request if you can...

If you have the Fox Cloud 2.0 app, and you click on the Battery icon, what do you see as your SoC/Remaining energy?
I am not sure if your system shows as 1 large combined battery, also near bottom of this screen you should see battery reserve values.

[StarryTissue]

I have a request if you can...

If you have the Fox Cloud 2.0 app, and you click on the Battery icon, what do you see as your SoC/Remaining energy?
I am not sure if your system shows as 1 large combined battery, also near bottom of this screen you should see battery reserve values.

Sure can here you go. It shows as one big battery.

[MaterialBarracuda48]

One massive battery, check... and the 13% SoC does equal 5.45kWh it claims is left.

In the same battery section, under your settings, what does that show?
Is your battery reserve and Sys min SoC both 0%?

[StarryTissue]

One massive battery, check... and the 13% SoC does equal 5.45kWh it claims is left.

In the same battery section, under your settings, what does that show?
Is your battery reserve and Sys min SoC both 0%?

Both battery reserve Sys min are set to 10%.

When the SoC reaches is 100% the remaining energy on screenshot 1 is 41.9kwh.

[MaterialBarracuda48]

I think it is your 10% reserve that is breaking your maths, as I was thinking earlier this morning.

41.93kWh total capacity
Discharge is 14.7kW, so naturally 14.7kWh.
Now 2hrs of constant discharge is 29.4kWh.

Now if we take the starting total of the full available 41.93kWh
29.4/41.93kWh = 70% so 30% SoC remaining.


If we now account for your 10% reserve value...
41.93kWh becomes available to use 37.74kWh
Plug in our used energy for 2hrs of discharge
29.4/37.74kWh = 78% so 22% SoC remaining.


Now if you set your reserves to 0% (as it does claim 100% full Depth of Discharge) then you should find the above maths will add up.

[StarryTissue]

I see what you are saying, and that would make sense if the SoC represented the total amount of the battery left- without the reserve. It would appear something like this:

• at 100% it the battery available was ~37kwh
• at 0% the battery available was 0kwh
• and the Fox battery still had ~4.1kwh in reserve

However when the SoC is 100%, the battery available says ~41.9kwh, and when the SoC reaches 10%, the battery available says ~4.1kwh.

I'll take a screenshot tonight to confirm the battery available each hour after discharging.

[MaterialBarracuda48]

I think the Fox Cloud 2.0 will be very black and white so to speak... you have xxkWh left in the tank (which it reads from the full capacity) So I think Fox will always show what your real capacity is for your whole system, but it doesn't remove the reserve.

I think the HA graphs are saying, you have reserved 10%... so it now reads what is available as lower in total, and uses this new lower value for graphing.

Not sure if you set the reserves down to 0% last night, and then are testing, hopefully this is what you did so it matches up.

[Dave Foster]

However when the SoC is 100%, the battery available says ~41.9kwh, and when the SoC reaches 10%, the battery available says ~4.1kwh.

I know for the Australian market the minSoC is allowed to go to 10% but for Europe it’s always been sold as a 90% DoD i.e. 10% minsoc cannot be reduced. The kWh remaining figure does indeed show everything the battery has remaining (including the 10% minSoC) it’s just we cannot access anything less than 10% as the BMS will cut power hence your actual kWh capacity would be 90% of 41.9kWh with a 10% minSoC.

Whilst i’m thinking about it, as your discharge rate is very high just to mention Fox ‘recommend’ a sustained 30A charge/discharge with a maximum of 50A. given your battery voltage range is 365V-463V a 14.7kWh sustained discharge would be 31.8A at 100% SoC, increasing to 40.7A at minSoC.

[MaterialBarracuda48]

I know for the Australian market the minSoC is allowed to go to 10% but for Europe it’s always been sold as a 90% DoD i.e. 10% minsoc cannot be reduced.

Dave, did you mean the Aussie market is allowed to go to 0%?
I did download the Aus spec sheet and it claims 100% DoD.

[Dave Foster]

I know for the Australian market the minSoC is allowed to go to 10% but for Europe it’s always been sold as a 90% DoD i.e. 10% minsoc cannot be reduced.

Dave, did you mean the Aussie market is allowed to go to 0%?
I did download the Aus spec sheet and it claims 100% DoD.

Yes apparently it does go down to 0%, I’m not sure whether the hardware is different or whether it’s the same LFP cells but with different battery firmware, all the European variants won’t allow being set that low and the warranty is based on 90%.

[MaterialBarracuda48]

Yes apparently it does go down to 0%, I’m not sure whether the hardware is different or whether it’s the same LFP cells but with different battery firmware, all the European variants won’t allow being set that low and the warranty is based on 90%.

Not sure if it has more cells/different cells either!
I am hoping OP will be along with some tests at different reserves, I suspect it all boils down as to how HA reads the capacity, I am thinking it is being "told" capacity from the BMS (Fox Cloud 2.0 reporting real)

We shall know in a day or two.

[StarryTissue]

Yes apparently it does go down to 0%, I’m not sure whether the hardware is different or whether it’s the same LFP cells but with different battery firmware, all the European variants won’t allow being set that low and the warranty is based on 90%.

Not sure if it has more cells/different cells either!
I am hoping OP will be along with some tests at different reserves, I suspect it all boils down as to how HA reads the capacity, I am thinking it is being "told" capacity from the BMS (Fox Cloud 2.0 reporting real)

We shall know in a day or two.

Hi all, these are the things I tested based on your comments:

1. Does the Battery SoC percentage in Home Assistant represent the total battery capacity less the Min SoC?
   No, it does not. It represents the total battery capacity inclusive of Min SoC.
   1. Test 1: Change Min SoC (on grid) and Battery Reserve to 0%
      1. I was able to change these two values to 0% on the main interface. However, in the mode scheduler you are forced to put Min SoC (on grid) back to 10%. It doesn’t let you enter a number below this. So when the force discharge begins, the Min SoC jumps back to 10%.
   2. Test 2: Confirm that the battery percentages on the Fox app match the same stat on Home Assistant at start and end of discharge
      1. I confirmed that the Battery SoC in Home Assistant matches what is shown in the Fox app. I also confirmed the Fox app battery percentage does not change based on the Min SoC level.
         Conclusion: Home Assistant percentage is unaffected by the Min SoC or Battery Reserve settings.
2. Does another force discharge produce the same results?
   Yes, another discharge produced the same results as before. Battery starts at 100% (in Fox App and Home Assistant) at 5:30 pm, and after 2 hours of discharge it is 21%.
   Other notes:
   1. Home Assistant also shows "Battery Discharge Today". In the 2‑hour period, that value goes from 8.3 kWh to 38.0 kWh, which equates to 29.7 kWh of battery discharge.
   2. 79% of battery discharge should equate to 33.1 kWh. So there is a discrepancy of 3.4 kWh.
   3. Battery percentage is rounded to the nearest whole number and only updates when the displayed percentage changes. So some slight rounding error is expected.

Happy to try any other tests. However, it seems like some capacity is missing for whatever reason.

[MaterialBarracuda48]

The crux of the problem is that you are using for all your calculation the full kWh capacity of your system, you have to understand that the system is "taking" 10% off you, that you can never touch/use.

As mentioned here...
If we now account for your 10% reserve value...
41.93kWh becomes available to use 37.74kWh

Take the top value of your image, by your calculation, you discharged a reported 33.1kWh in 2 hours, so that's 16.55kW.
The bottom graph shows that same discharge rate of 14.75kW. If you repeat your calculation at the top, this time taking off the 10% that is reserved.

79% of 37.74kWh then becomes 29.8kWh used, so becomes 14.9kW flow rate (remember there will be losses for DC->AC here, so that might make it 14.75kW that goes out to the grid.


For your bottom equation, once again you see that your graph shows that the battery used a delta of 29.7kWh (at the top you state 33.1kWh, both cannot be correct!) Given the system shows a REAL use of 29.7kWh, then once you input this into the calculations...

29.7/37.74 = 79% rounded (which matches the top of the image for SoC delta.)



An analogy that might help is understanding that if you had 41 cup cakes, and for whatever reason, you have 10% taken off you as some sugar tax (heaven forbid!) so now you are left with 37 cup cakes.

If you eat 50% of the cup cakes, is that 50% of 41 or the actual 37 cup cakes you have?


Now, the kicker.. if your battery is sold in the Australian market with 100% Depth of Discharge and you cannot set this value... that's either a regional setting in your inverter that is not working, a bug in HA that will never allow the value to be at 0%. Solution would be to present this to Fox and get them to upgrade the firmware to allow 0% (if the fault lies there) or HA could have a bug that will not allow less than 10% to be used (well the maker of the HA integration?)

[StarryTissue]

All makes sense and thanks for the detailed response! Just to clarify yep am in the Australian market.

Understand what you are saying and your calculations makes sense. However, assuming your theory is correct it presents some contradictions:

• 1. Using only the Fox app, when the battery says 100% it also says 41.9kwh as "Remaining Energy" right below it. When the battery gets to 10%, it says 4.1kwh as "Remaining Energy". That indicates the reserve value is included in the figures when using percentages.
• 2. If the Remaining Energy is displayed incorreactly and it is a bug in the fox app: at 100% SoC, the Remaining Energy should be 37.7kwh (as opposed to the 41.9kwh), and when it gets to 10% it should also say ~3.8kwh (as opposed to the 4.1kwh). If that were the case, the software doesn't allow discharging that remaining 10%. That would mean Fox is not allowing use of 19% of the battery capacity (a. 100% * 10% = 10% of battery reserve, and then b. 90% * 10% = 9% due to the software limitation).

So in either case, there is either something wrong with the app figures, and in both cases, we aren't able to access the full battery as specified. At best we are missing 10% capacity, and at worse we are missing 20% capacity.

All can be reproduced using Fox Cloud stats, home assistant is just a handy way of graphing and logging that data at a good higher interval. So I definitely don't think it is a home assistant issue.

But as you suggested will write to Fox and see what they say.

Hope that all makse sense! Again appreciate the response in trying to figure this out!

[MaterialBarracuda48]

I guess it is now a waiting game to see how Fox support can handle this for you