Hi all, I had solar panels and a fox h1g2 inverter and fox ep12 battery installed around 6 weeks ago, but over the last 2 days I've noticed it has been force charging itself overnight whilst set to self use mode. My force charge schedule has only 1 timeslot set up and that is 2am to 5am, to reach 40% Soc, but that is currently toggled to the off position. My battery charged itself from 10% to 26% yesterday morning around 7am, then charged itself to 40% at around midnight, and charged again to 45% at 4am. After the first battery charge I set my pre heater to 4° as it has got cold recently. (down to 0 - minus 1 or 2 °)
I thought this would eliminate the charging itself issue, but it hasn't.
I'm currently on a fixed rate tariff whilst I wait for my DNO letter to arrive, thats why my battery is down at 10% Soc a lot of the time.
Can anyone offer some advice please?
Lee
Here is a long read, viewtopic.php?p=6448#p6448 I was waiting for the first cold snap to see a post 
In short, the battery BMS will do a maintenance charge IIRC below 5°C or some low temp like that to protect the cells. This will charge no matter what work mode you are set to.
I suggest you increase that start temperature for the heater to 9°C and end at 15°C (you can adjust those start end points of course) those values worked best for me, as the battery charge AND discharge rate changes with certain temperature brackets, so you want to keep it in the goldilocks zone.
In short, the battery BMS will do a maintenance charge IIRC below 5°C or some low temp like that to protect the cells. This will charge no matter what work mode you are set to.
I suggest you increase that start temperature for the heater to 9°C and end at 15°C (you can adjust those start end points of course) those values worked best for me, as the battery charge AND discharge rate changes with certain temperature brackets, so you want to keep it in the goldilocks zone.
It’s usually a strong indicator that the lowest cell in your battery is very cold and the BMS will start a slow maintenance charge to raise the temperature. It’s both temperature and SoC dependent so will not do it at higher charge levels. Once you have your low tariff, force charging at night will warm it up and the higher state of charge should avoid the issue.
I don’t use battery warmup myself, but I believe that most people set the temperature to around 9C as at 4C it’s getting too close to the battery discharge shutting down which at low soc’s will be what’s doing the bump charge.
EDIT : @MB, sorry you just beat me to it
I don’t use battery warmup myself, but I believe that most people set the temperature to around 9C as at 4C it’s getting too close to the battery discharge shutting down which at low soc’s will be what’s doing the bump charge.
EDIT : @MB, sorry you just beat me to it
Well I'm glad I'm not the only one, seems one of the cells ("Min. Cell Temp") was below some threshold at some point (it's barely above 4.1C now at 10 AM). The inverter temperature hit a low of 3.6C at 2 AM, but Battery temperature remained above 13C. So I assumed it had something to do with temperature.
It started charging at 2 AM until 4, then again at 7 AM until 8 AM when the PV started to pick up the early morning sun.
I will enable the battery heating and set the time period to charge during lowest cost period in the night and keep an eye on it. It would be useful if the running state or some other status explained why it forced charging, the inverter status remain as `on-line` and the running state was `163: on-grid`.
It started charging at 2 AM until 4, then again at 7 AM until 8 AM when the PV started to pick up the early morning sun.
I will enable the battery heating and set the time period to charge during lowest cost period in the night and keep an eye on it. It would be useful if the running state or some other status explained why it forced charging, the inverter status remain as `on-line` and the running state was `163: on-grid`.
The on-line status doesn’t show it, but if you track the ‘Max Bat Charge (or Discharge) Current’ you’ll likely see the effects of temperature as the BMS throttles the charge.WelshProgrammer wrote: ↑Fri Nov 13, 2026 10:15 am I will enable the battery heating and set the time period to charge during lowest cost period in the night and keep an eye on it. It would be useful if the running state or some other status explained why it forced charging, the inverter status remain as `on-line` and the running state was `163: on-grid`.
I'll dig in the API and see if it's returned, just not extracted.
Cheers, WP.
Sadly it isn’t, but you can get them via modbus if you want to change your implementation, Fox said they would provide them but then decided against it (I suspect the BMS algorithm may be a bit flaky on some battery firmware), they provided the Max Bat sensors instead as a concession.WelshProgrammer wrote: ↑Fri Nov 13, 2026 10:44 am Screenshot from 2026-11-13 10-42-37.png
I'll try to find some way of correlating these in HA. Shame the FoxESS HA doesn't expose the Min Cell Temp (or at least it doesn't in my setup). That would probably be the key in tracking this.
I'll dig in the API and see if it's returned, just not extracted.
Cheers, WP.
I've found minimum cell temperature on my Evo is exposed in register 37618, under BMS cell temp low
I had to add my model manually to entity description.py under that. Try it on read register first to validate.
I had to add my model manually to entity description.py under that. Try it on read register first to validate.
7.36kWp solar array made of 16x Jinko Tiger Neo 460w panels. 8 ESE, 8 WNW facing, Fox EVO 10kWh with 10kW inverter. Installed April 2026. Running ModBus via Elfin EW11A, learning Home Assistant
Hi,
Thank you for your responses, I will change my heater settings to 9° minimum.
I contacted my installer , who then contacted Fox, and they did a firmware update on the inverter, but that does not seem to have fixed it. My battery self charged at 31% upto 45%, at 00.20 and then charged again at 05.30 from 33% to 41%.
Installer said to contact them again if it continues. So, an email to them is incoming....
Thank you for your responses, I will change my heater settings to 9° minimum.
I contacted my installer , who then contacted Fox, and they did a firmware update on the inverter, but that does not seem to have fixed it. My battery self charged at 31% upto 45%, at 00.20 and then charged again at 05.30 from 33% to 41%.
Installer said to contact them again if it continues. So, an email to them is incoming....
I would hold off that email Lee, and change the temperature first (like you mentioned to min 9°C) and see if that sorts the emergency charges.
If you have cheap overnight tariff, you can program those times in, and overnight is when it is typically the coldest. I would also sort some insulation out too, as this is better in the longer term.
Good luck.
If you have cheap overnight tariff, you can program those times in, and overnight is when it is typically the coldest. I would also sort some insulation out too, as this is better in the longer term.
Good luck.