FoxESS Community - Owners & Installers Forum

My EP11 is set up to grid charge only from 23:30 to 05:30 because I am on the IOG tariff and that has worked well for months.
It's certainly cold but it did charge fully overnight both times.
Suddenly it has started charging from the grid at other times.
One day it discharged down to min SoC around 12% by 3pm then started to charge up until nearly 9pm then discharged until 11:30pm, the correct charge time.
The other day it discharged down to 12% late morning, then at 13.30 started to charge for 4.5 hours to 60%, discharged for 2 hours to 20% then charged again for another 3.5 hours.
All the above are outside the set charge rates and interestingly all the charges are at exactly 0.84kW which makes me think it's a setting in ther BMS?
I've checked the inverter and no fault logs and date/time are correct?
I have the battery heater set to come on on the low tariff hours as well.
Anyone got any ideas why?

Edit Just noticed the same thing has just started for the third day!

The 0.84kW suggests that your BMS has initiated a maintenance charge request, that is usually because the minSoC has fallen too low (i.e. below the minsoc from grid setting), or the temperature has dropped so low that it trying to protect the batteries.

Thanks, I thought it might be something like that.
I tried upping the min SoC to 12% yesterday and today it dropped to 11% at 10am, and stayed at that till just before 2pm when it started the maintenance charge again.
Will raising the min SoC help prevent that?

However yesterday evening it did the same thing but the SoC was still at 20%.

As a possibly related issue, the Fox app is showing warmup on standby with a temperature of 3.1C, but my Home Assistant is showing the battery temp at 15.7C and the inverter at 8.6C.

With the current very low temps should I keep the heater on all the time?

No raising the minsoc wouldn’t help and might make it slightly worse because as soon as it gets close the battery maintenance charge cycling will start.

The EP11 heater should be enabled to warm the batteries in the coldest part of the night when you are not charging, but worth checking your battery firmware is up to date as there are a lot of posts at the moment about odd heating behaviour with earlier firmware.

Charging overnight in the IOG timeslot will warm the batteries anyway so heating before 23:30 and after 05:30 would be helpful - the batteries charge slower if the temperature is low which means they may not get to 100% in the 6 hours.

appman999 wrote: ↑Mon Jan 05, 2026 2:39 pm As a possibly related issue, the Fox app is showing warmup on standby with a temperature of 3.1C, but my Home Assistant is showing the battery temp at 15.7C and the inverter at 8.6C.

Your BMS Cell Temp Low value as seen in this post is your cell temperature, this is what your Fox App is correctly reporting to you. The 15.7C you are reading is for the BMS chip itself
viewtopic.php?p=11800#p11800

appman999 wrote: ↑Mon Jan 05, 2026 2:39 pm With the current very low temps should I keep the heater on all the time?

If you are using IOG like me, have 2x charge from grid slots enabled
Slot 1 23:30 to 23:59
Slot 2 00:00 to 05:30
Slot 3 00:00 to 23:59 <-- You can disable Slots 1&2 and enable this one if you wish 24hrs heating, but note when heating you loose charge/discharge abilty currently for an hour or so when it heats.

Current behaviour is my current values will heat it up enough to reach 100% SoC by the 05:30 end of cheap IOG on an EP11 (in unheated garage) Then during the morning when there is enough PV available, and it needs heat... it will use PV, do doesn't need grid 24/7 enabled.

Thanks, I am already set up with heater on slot 1 and 2 as you suggest and it worked fine until 2 days ago, charging full overnight.

But battery only lasts the morning so I expect to run house using grid then, but instead it also randomly charges the battery during the afternoon (at full cost!)

When I saw today's random charging starting this afternoon, I turned on the heater which promptly stopped the recharging!

As Dave suggests it must be some kind of maintenance charge due to the cold weather so I need to have some random heating cycles to keep the battery temperature in an acceptable range (whatever that is)

Gotcha, so it was doing an emergency type charge then.
I presume your battery lives outside then?

Correct

Exactly the same is happening to mine, and I have the same set up as you. I was wondering about building my battery a cover to reduce the impact from the cold. But I'll try adding more heating periods and see if that helps.

Update: Turned on heating and it didn't stop charging. Battery temp up to 4.7 from 2.8

Same thing happening with me. Had suspicion about effects of cold (currently -7 outside in UK) but as a relatively new owner I equally thought it was operator error on my part.

Is there a thread I should look at for suggested settings for a pair of EP12 with 10kw Invertor using IOG tariff? I've fumbled my way to set-up but likely done it correctly especially with regard to heating.

Maybe needs a min temp it has to reach to stop charging from grid, maybe 5C?
Unfortunately can't find a way to get history of temp to match when unwanted charging starts.

Now up to 11 C and still charging. But the heating icon on the app has changed from standby to arrows moving, so something is happening.

Have also submitted a ticket to Foxess as may need FW update. The other day it decided to stop discharging at 50% for no reason. Could be an expensive January.

Model：
H1-3.7-E-G2
Version_Master：1.33
Version_Slave: 1.03
Version_ARM：1.49

JaseP13 wrote: ↑Mon Jan 05, 2026 9:08 pm Same thing happening with me. Had suspicion about effects of cold (currently -7 outside in UK) but as a relatively new owner I equally thought it was operator error on my part.

Is there a thread I should look at for suggested settings for a pair of EP12 with 10kw Invertor using IOG tariff? I've fumbled my way to set-up but likely done it correctly especially with regard to heating.

It may not be operator error, plenty of little bugs to keep us entertained.
If you prefer to make a new thread with your own questions, then you can get personlised answers, or I can reply here if you wish?