FoxESS Community - Owners & Installers Forum

Hi everyone,

Apologies for the long post, I have had a new solar panel + battery system installed via my local council's Solar Together scheme, and the battery and inverter have unexpectedly had to go outside. I've had little to no guidance from the installers and there seems to be no Fox end user guide or manual, only installation guides. And although Fox do respond to tickets raised very quickly, I can't exactly raise a ticket saying 'teach me how to use this and keep the battery warm'. So I'm a little desperate for some assistance.

Initial surveyor wrongly informed me the battery and inverter could go inside the house. A few days before installation I was told this is against the fire regs of the scheme, so on the day, with no guidance or knowledge, I had to pick somewhere outside on the wall of the house. This means I have a completely uninsulated battery outside that, although rated to be weatherproof outside, which is a positive, it slows to trickle charging in the cold, and for the last two nights has switched off discharge until well after midday the next day as it won't warm up. Installers basically told me how to download the app, warned me 'the battery won't work in the cold, that's normal, not a fault', and left me to it.

I have now scoured the internet for a week or more, and I gather the battery will throttle charging significantly according to temperature - I saw a helpful table on this forum, and I think I have this part figured out. Hopefully this means in summer everything will be great, as the system is installed on a north facing wall, and should stay within the good range even in our increasingly hot Midlands UK summers. However, the battery temperature (not ambient temp) is going down to as low as 2C overnight in this winter, which seems to prompt a charge from 10% SOC to 60% overnight from grid, even though charge from grid was disabled. Add the cost of this charge to the fact that I'm then not able to use the solar the next day to charge the already nearly full battery (as there is so much it exports to grid), plus the battery takes a long time to warm up enough to discharge, and I'm concerned I've been sold a system that is going to be next to useless for my needs through winter. I had planned to use overnight cheaper tariffs to charge the battery and (in future) an EV. Not great if the system throttles the charge/won't discharge on just averagely cold nights, not even deep frosts.

Some initial questions:
- At what temperature does the battery shut off discharge? And how can I prevent this happening?
- Is the automatic 10% SOC charge from grid to 60% a known reaction? Will it happen every cold night? Is there a set temperature this process is triggered? And can I prevent it in any way?

- I watched a very useful video from Will on here about insulation solutions. Unfortunately, I do not have 300mm around the battery to construct insulation (see image - any insulation structure would extend across my windows and into the garden gate/downpipe/water butt to the right). Nor am I able to do much DIY for reasons I won't go into. How can I insulate the battery? Ideally with something temporary that I can put over the battery through winter, then store in my shed the rest of the year. Every solution I can find online seems to involve building a shed around it (not possible) or is for internal/loft solutions and involves constructing a cube of non-weatherproof foam substances (presumably not ideal outdoors). Any other suggestions I've seen online seem iffy at best, e.g. putting on lagging of the sort you might put round a hot water tank, insulated covers of the sort you might tie over garden furniture... Any cheap and easy to handle suggestions gratefully received.

Thanks for any help you can give,

Marc

This is not a great way to start out with solar, i’m sorry to ask but i’ll need to ask quite a few questions as well as answer those you have.

If you can raise support tickets can I assume you have access to the system via the V2 app or the Foxesscloud website i.e. you have been given credentials to log on ?

If so it would be useful to know what your battery settings are (minsoc, battery reserve) and also to know if you have any charge periods set.

Being mounted outside without any enclosure is not ideal as you are seeing, the battery will start to throttle the charge current below 20C with the biggest effects happening below 10C. At 0C the batteries will no longer charge until they warm up again but they may discharge down to as low as -10C depending on their state of charge.

The batteries may attempt a low power maintenance charge to raise their internal temperature in order to keep them operational and that may be the charging behaviour you are seeing - if they are dropping to 2C that is certain.

The usual approach as you have said is to provide an insulated enclosure, they can be more complex like a wooden insulated shed or as simple as an insulated box but in all honesty 50mm kingspan insulated sheet to forming a box underneath and around the battery using duct tape would be help in freezing temps. Because of your size constraints this would have to be removed in the warmer months because of the lack of ventilation but it would be needed in place between December through February to give them some protection.

Does your EP5 battery have a label on the side where the serial number is that that says ‘WARM’ ?

Thanks for the quick reply Dave, and no problem, ask away! I should say, I'm happy with the setup generally - I'm generating lots of solar, I'm quite a low user of electricity currently, and my daily usage bill is already significantly lower, so I'm aware that anything I generate and store is better than not having solar at all! But mildly frustrated with the storage side of it.

Yes, I'm on the V2 app and I think I understand how to work everything on there. Got my firmware updated straight away based on posts on here. App seems fairly intuitive. No charge periods set currently (though for a couple of days I set it to fully charge from the grid, then discharge fully through use, based on a previous post of yours suggesting it would help the battery get working), Minsoc 10%, Battery reserve 10%. Battery reserve was 20% by default, but that caused a drain overnight to about 15% (while the grid powered the house load, it was weird, as if the 20%-15% charge just disappeared!) then charging from grid back up to 20%, which I saw as needless cost, so I reduced it to match the minsoc. One thing the installers have told me gave me the impression the battery would just sit at a certain SOC (perhaps the minsoc?) overnight, such as the minimum, or only use a little amount to run the load overnight, whereas I seem to be seeing lengthy charging overnight as mentioned previously.

No sticker saying WARM anywhere I can see.

Discharge definitely was not working yesterday and today overnight and until about midday, at cell temps no lower than 2C, and then discharge only seemed to go back up to the standard 20A once cell temp was about 4C, which was only after solar had trickle charged the battery for several hours. Keeping tabs on this in Detailed Parameters in the app. Battery discharge remained at zero yesterday even at 60-70% SOC and drawing load i.e. when it should have started using the solar first and then the battery as well, but instead drew from grid. Temperatures nowhere near the -10C which the sticker states it might continue to discharge down to.

Battery currently has about 80% SOC so will check in in the morning, I'm assuming it won't need to charge overnight as cell temp is still as high as 5.7C now, it has been charging all day from solar so is warmer.

Ok it sounds like you have a good grasp of the system, the EP batteries are a (relatively) new range and their charge/discharge parameters appear to be stricter than other battery systems, but this has happened with all of the Fox batteries, they release it with ‘the safeties on’ and gradually improve it when they have real world data on their performance.

It does not surprise me that at prolonged low temperatures below 2C they close down - the reason I asked the question about ‘WARM’ is that because of the trend to install batteries outside they have concluded that all of these batteries will perform better with internal heaters. The idea being that a small amount of contained heat within the battery cells will be more effective than forcing them to float charge to raise the temperature. - this is all very new and only just getting traction but it seems to work.

We’re probably nearing the end of the prolonged low temps (never say never) but the only meaningful solution in maintaining battery temps is to insulate the battery. As you have read Fox want 300mm air gap around the batteries - their guidance is based on continuous use all year like that, it is entirely practical to add insulation sheets around the battery for short use as long as they are removed when ambient temperatures (and solar generation) increase - but you have to be responsible for doing it.
Note : Fox monitor the batteries so as far as warranty goes they will know the extreme highs and lows the battery is exposed to (less of an issue here in the UK but they are a global company and I regularly talk with people where the ambient temp is >40C most days so you have to think through any guidance they give.)

LifePo4 batteries (LFP) whilst affected by low temps are not damaged by it, they will return to capacity as soon as warmed up, however they will be damaged by prolonged excessive high temps ~55C and that will reduce their lifetime and capacity.

One last point to mention, the inverter firmware and battery firmware are distinct and usually one is updated without the other - if you ask for the firmware to be updated the support teams usually imply inverter not battery - so it is possible that your EP5 is not as up to date as it could be - you can check in the V2 app by going to Device, Battery, click the serial number below the picture of the battery - the BMS version is the version running on your EP5 (the EP range only has a single version of firmware not master/slave as the older batteries did). If you post back what you have i’ll look up the latest for you,

Thanks Dave - great help. Overnight last night, the ambient temp got down to 0C, but the battery (possibly as it still had plenty of charge) only got down to about 3C, and continued discharging all night and this morning despite the cold. Although interestingly the discharge current has fallen from 20 this morning to 10 now. But it does seem like it performs better at keeping the discharge function on when at a higher SOC. I wonder if that's what others have found? Barely any solar coming in today so tonight will be another learning night as the battery approaches minsoc.

I will look into that 50mm Kingspan sheeting - some sort of removable, vaguely rainproof 5 sided box I can shove against the wall for winter sounds ideal. Location is fairly sheltered although not under a roof. I will see if I can tap up a mate with some tools and the capability to construct something. Have you done that kind of setup yourself, or seen it done? How would I fix those sheets together? Appreciate construction might not be your area of expertise

Just to confirm, I think I read elsewhere that it's just the battery that needs insulating. The inverter is fine to be left open. Is that correct?

Battery firmware is version 1.004. Please let me know if that needs updating.

March wrote: Wed Feb 19, 2025 11:12 am Thanks Dave - great help. Overnight last night, the ambient temp got down to 0C, but the battery (possibly as it still had plenty of charge) only got down to about 3C, and continued discharging all night and this morning despite the cold. Although interestingly the discharge current has fallen from 20 this morning to 10 now. But it does seem like it performs better at keeping the discharge function on when at a higher SOC. I wonder if that's what others have found? Barely any solar coming in today so tonight will be another learning night as the battery approaches minsoc.

I will look into that 50mm Kingspan sheeting - some sort of removable, vaguely rainproof 5 sided box I can shove against the wall for winter sounds ideal. Location is fairly sheltered although not under a roof. I will see if I can tap up a mate with some tools and the capability to construct something. Have you done that kind of setup yourself, or seen it done? How would I fix those sheets together? Appreciate construction might not be your area of expertise

Just to confirm, I think I read elsewhere that it's just the battery that needs insulating. The inverter is fine to be left open. Is that correct?

Battery firmware is version 1.004. Please let me know if that needs updating.

In all honesty i'm not 100% sure on the discharge rates particularly on the EP batteries as they are so new that chart has not been published (or worked out), as a general statement I can say that as the SoC falls lower the discharge rate will be reduced - so worth keeping an eye on the discharge rate over SoC and temperature to fill in some of the blanks.

The 50mm Kinspan (or Recticell etc..) is very rigid and stands up on it's own, whilst my batteries are sat on insulation and lifted off the floor with 4x2" beams I have them surrounded by 50mm insulation sheets and a piece on top with cable cutouts - all held together with duct tape - this stuff is extraordinarily strong and will hold the edges together really well https://www.amazon.co.uk/dp/B0BXB7X9HZ?th=1 - it holds together well and can be taken apart when needed.

It is just the battery that needs insulation, the inverter is air-cooled via the rear fins and will get hot when worked hard (when charging or lots of solar generation) so having good air flow is important.

Your battery firmware is behind (not by much) but as these batteries are so new I would say definitely get it updated - if you raise a ticket on Fox and specifically ask for them to update your battery firmware.