Battery Insulation/heating?

[Ched]

I have 2 x hv2600 batteries in my loft and they are getting too cold to charge and discharge.
I was thinking of making an insulated box out of 50mm of polystyrene. Is this ok or is there a better way?

Cheers for any suggestions.

[Dave Foster]

The community has come up with many elaborate solutions for this (me included) - 50mm Kingspan would be better, but anything is better than nothing.

Make sure you maintain an air-gap (officially 300mm) and make it such that it can be removed when the weather warms up in June/July/August as getting too hot (>50C) is worse than too cold.

[calum]

We had our system fitted almost exactly a year ago, and the unprotected batteries stopped working several times during the cold snaps we had last winter. I built the box in mid January, and after that everything worked pretty well, although we probably weren't getting the absolute best capacity out of the batteries. I suspect a lot of that was more down to firmware than temps, though.

If I were doing it again (or advising someone else!) I would say make sure you insulate all six sides, allow for internal air circulation, and ideally allow that air circulation to become air throughput if needed - potentially allows you to duct in cooler air from outside if elevated battery temps are a concern.

I bought the 25mm sheets of EPS in a pack because a) they would fit in my car easily and b) it was the cheapest way to get the amount of insulation I needed. I cut them up to fit on the OSB panels. The back panel of the box (not visible in the photo) only has 25mm of insulation, because otherwise it doesnt fit! It maybe that is part of the reason for the variance in my case, there are individual cell temp values available in the Foxess website, and I daresay I could work out which cells are at the front or back of the banks, but we'd be well into diminishing returns at that point. But I put the box together in the garage and all the other panels got 50mm of insulation from the off, so I can't really say how much difference it would have made vs 25mm (or 50mm!) all round.

If you're going to the trouble of getting up into the loft and building an enclosure, I'd go with 50mm to begin with. How warm did your batteries get in the summer? if you expect to need to dismantle the thing to allow them to cool, I'd aim to add some hard materials to the outside, otherwise just making it out of insulation will likely fall to bits after a few seasons, especially with EPS. The Kingspan polyurethane stuff might do better but I'd still suggest you do something structural even then. I did 9mm OSB for lightness, with battens on the corners and threaded inserts and bolts so it won't mind being disassembled and reassembled.

I couldn't get a big sheet of 50mm Kingspan into the car, so I went with the EPS. It works fine, but it's quite crumbly when you cut it. The official guidance does indeed say 300mm air gap all around, my box has something like 25mm at the back and sides, more like 100mm at the front as it has to make room for the cables. I was fully prepared to dismantle it for summer but I've also been keeping an eye on the temps. It's been completely fine and overheating has never been a problem, I just prop the lid open in the summer. BUT that's in a cool shaded garage with a lot of thermal mass to regulate temperature changes.

In a loft you don't have the same thermal mass, and of course they can get really hot in the summer. Even without an insulating box, during a long spell of warm weather I could see your batteries getting uncomfortably warm. So again, if I was doing this in your situation but knowing what I know, I'd be looking at arranging to duct cool(er) air in from the outside and passing it through the battery enclosure.

During cold weather you'd still want to circulate air within the enclosure to keep temps as even as possible. Ideally you'd be able to use the same fan for this as you were using for throughflow in the summer, but this is already possibly a bit overengineered.

EDIT: I didn't explicitly mention heating, given that a 40W tube heater from the likes of Dimplex is relatively inexpensive, combining that with a fan and the built in thermostat definitely seems worthwhile. My enclosure is currently unheated, thus far the tactic of spreading the heat from charging and discharging around with fans is keeping the "Low Cell Temp" above 15C, but I can see the amount of charge it accepts starting to drop a little, so I'd not want it to get much colder than this.

All that said, these batteries are costly and resource intensive to manufacture, I think it makes good financial sense (as well as moral and practical sense) to look after things and give them as long a working life as possible.

[Ched]

Cheers everyone.
I nipped out to Wicks as they had smaller sheets that would fit in the car, the kingspan they had was either 2400 x 1200 or 1200 x 450 which would have been better it it were 1200 x 600.
I ended up buying 3 x Jablite HP+ External Wall Insulation 70 Expanded Polystyrene Insulation - 1200 x 600 x 50mm at £10 each. Just cut 2 of them in half so 600x 600mm then created a box with that and some 50mm gaffer tape. Then cut the remaining one to make a lid. Couple of slots for the cables and looks good for the winter. I will keep an eye on the cell temps over the coming days and probably remove it in spring. It's very easy to get at as we have a dormer bungalow with a small door to the loft space and the batteries and inverter.

It's not perfect but it will do till I can monitor the temps and see how we go.

Thanks again.

[Ched]

OK so it's not even been 24 hrs since I fitted my insulating box and the battery temps are so much better. After a full charge overnight the cell temp was 28.7C and at 12 midday today it's down to 21C so not too bad at all. The batteries charged at their full rate which is great. Looks like a box of 50mm of polystyrene (chipboard floor under batteries) in a loft works fine.
I will continue to monitor the battery temps as the weather warms up a bit.
Cheers

[calum]

Out of interest what are the ambient temps in your loft?

[Ched]

Out of interest what are the ambient temps in your loft?

Just had a quick check the loft is about 4 deg C, outside is about 2 deg C, batteries currently on Self Use at 25.2 deg C = BMS Cell Temp Low.

[Janfil]

Someone has recommended to me that I wrap heating wire round my outside wall mounted battery which has gone into hibernation numerous times this winter. The heating wire is what is sold to wrap round water pipes to stop them freezing and comes on when a predetermined low temperature is reached.
Anyone tried this, or any comments?

[Dave Foster]

Someone has recommended to me that I wrap heating wire round my outside wall mounted battery which has gone into hibernation numerous times this winter. The heating wire is what is sold to wrap round water pipes to stop them freezing and comes on when a predetermined low temperature is reached.
Anyone tried this, or any comments?

I've not heard of anyone doing that but I would have thought it might take a lot of wire, quite a lot of power and if exposed to the conditions probably not be that efficient.

When charging the batteries do generate quite a bit of heat and just containing it is usually enough to overcome most of the cold weather effects.

What most other people do is to build either temp enclosures i.e. Kingspan insulation board around and over the batteries (which keeps any heat generated by the batteries during use in the enclosure), or a more full time enclosure that protects it from the elements and allows insulation to be fitted in winter, and removed in summer to allow ventilation.

[CDubbs]

To anyone who has built an insulated cover around the battery, did you fully insulate all sides etc and if so have you allowed any ventilation for winter use or not ?

Thanks

[Frankie]

I have had the same issue with my battery but only this year.
After contacting FOX ESS their replied was that they set the limits of the battery so that it needed at least 15 degrees before charging fully.
They wrote:
We’ve checked the system behaviour, and the reduced charge rate is actually being triggered by low cell temperature, rather than a fault with the inverter or battery.
When the battery cell temperature drops below around 15°C, the BMS automatically limits the charge and discharge current to protect the cells. This is a normal protection mechanism built into the ECS series, and it will reduce charging power until the battery warms up again.
This is also why you are seeing slower charging in the morning and occasional excess export — the system is simply preventing the cells from being charged too aggressively while they are cold.
This current limit is a new safety feature added this year for certain battery models, which is why it didn't occur last winter.
The solution we can offer is to replace the battery master unit. This should resolve the current restriction.

So I have asked for a battery master unit replacement.
In the mean time I used 50mm Kingspan to insulate the battery and the temp is now up to circa 20 degrees while the ambient loft temp is around 5 degrees.

[CDubbs]

Thanks Frankie

Actually I’m not seeing that restriction under 15C

Last night batt temp was 9C and it charged at 5.75k, even though I’d restricted the inverter to pull no more than 3K,
So the whole issue is one of confusion.

[Frankie]

This is what a circular from Fox ESS from China stated.

Declaration
FOXESS CO., LTD.,which located No.8,Xiqin Road,Xinwu District,Wuxi,China,214028 as a
manufacturer of ECS series batteries:
Model:
FOX ECS series batteries
FOX ECS series batteries use high safety, long cycle LiFePO4 cells. This battery cell is characterize
d by a limitation of charging and discharging currents in low temperature environment.
Below 15°C, the battery charging ability starts to weaken, the lower the temperature, the weaker
the charging ability of the battery, and charging is prohibited when the battery is below 0°C.
Suggestion: In order to ensure safety, please install the battery in a place where the temperature
is suitable for use.
FOXESS CO., LTD.
Address:No.8, Xiqin Road,Xinwu District,Wuxi,China,214028
Bruce
Director of Product Dept
Date:2025/3/10

When I asked Fox ESS UK why this was not communicated and why they restricted their answer was:

To be honest, the exact internal reason for this adjustment hasn’t been fully communicated to us either. What we can do on the support side is quite straightforward — if any customer is not satisfied with this protection feature, we can offer to replace their unit with the latest battery model that does not include the current-limiting behaviour.

This is what I opted for so I don’t have to insulate my battery and all would work like it did last winter.

[CDubbs]

Thanks but my battery is an EP11 with a heater

[Frankie]

That’s why you are not having the problem.
The issue seems to be with ECS batteries which had their parameters changed but no one seems to know why.

[calum]

Even if the system restriction can be removed, I would still say insulating the batteries is a good idea. The electrochemical processes of charging and discharging are just more effective when the battery temperature is in the right range. And as has been mentioned, trying to charge the battery when it's cold will damage it.

My system has been in three years now, and the insulated enclosure I built has just been left in place, since the garage is on the north side of the house and stays relatively cool, even in summer. If I was doing it again I would also insulate under the batteries, but I'm not going to tear the whole thing to pieces just to do that. If you are insulating, putting some small fans inside the enclosure to circulate the air and even out the temperatues across the packs (if applicable) is a cheap and easy mod that helps to keep them balanced.

[CDubbs]

Thanks Calum

My battery is outside, and it’s got a metal cover round it, which gives 300mm internal air gap and ventilation , so I will just build a 50mm insulation cover around it fully, and monitor the battery temp.
In my case it’s something I would remove in the summer.