FoxESS Community - Owners & Installers Forum

I feel like I have the wrong size inverter specified in my new Fox installation. My inverter is an H1 G2 6kw and the strategy was to fully charge taking account of 10% reserve 4xEP11 batteries during my octopus 6hour off peak period. The maths works. I use 50/60kw/day in my house so we fully discharge during the day. However we had EP12 batteries delivered and the inverter only ever charges at 5.92w max and sometimes less. In reality my EP12 batteries are 46kw and if I take of 10% for reserve I’m 41.4kw requiring at 6.93 of inverter capacity - is that right - even with the ep11 batteries a 6kw inverter would never have got to 100% charge - is my logic right and what should I do ?

The maximum rate the H1-6.0 can charge at is 6kw AC which after conversion losses would be the 5.92kW you are seeing - the charge rate is affected by state of charge and temperature and so as it approaches 95% the battery will throttle charge to allow balancing as it approaches 100%, likewise a temperature below 20C will see similar throttling results falling to near zero below 5C.

If you have 4 x EP12 batteries, you are correct your max capacity is 46.08kWh but with 90% depth of discharge the useable capacity is 41.47kWh, which under ideal conditions would need an inverter capable of charging at 6.84kWh.

All of that said, to do what you want to do your existing inverter is under-sized and more likely you would be better with a KH inverter (available in 7, 8, 9 or 10 kW versions), to meet your needs across a wider temperature / SoC range you really want the KH10.

Thanks this is very helpful-whikst i will discuss it with my supplier i think i have indeed ended up with the wrong inverter which would never have worked - given that i had glowgreen as the supplier, would i need to go back to them to upgrade the inverter or can i simply just install a 10KW inverter and how much do you think it would cost - also is there a separate DNO application needed? Appreciate any thoughts

For warranty and continuity reasons, it would be much better to negotiate with your original supplier - however if you have all of the documentation for your system, you could use another supplier to retrofit the inverter but it will need another G99 application to be made.

To replace the inverter itself, the *cost* to purchase is ~£1,200 but you have the installation time on top and very likely the cabling, isolators and MCB/RCD’s would need to be replaced as well, as I say much better to come to an accommodation with your supplier.

Thanks and good advice - I have raised an issue with the supplier expecting them to come back in just such a way but their operations team were less than accommodating but hopefully they will reflect on this and we will reach a mutually agreeable position that makes everyone happy !! At the moment though I have a system that is teething ( which I expected ) but which would never have fully charged my batteries which I was not expecting. The operations team response was change power provider to one with 7 hour offpeak which actually no longer exists - let’s see

Just checking, are you using Intelligent Octopus Go, and if so, do you get some slots outside of the 6hr offpeak? If you do get some offpeak slots, do you charge house battery via automation or not at all?

Ideally it would be nice if the company can come to a mutual agreement on the system, and you get a bump up to a KH10 for a resonable cost.

Gotta ask, what are you using that many kWh per day on?

Hi great question and yes I do have intelligent octopus go but don’t know how to pick up auto battery charging when the off peak tariff cuts in during the day. If you have any guidance that would be great.

As to why we use so much power. We have a base load of 1.8kw - I know that I have 300w in my WiFi and cctv rack plus UPS and possibly some leakage from UFH pumps and in house ventilation - but working on that . In addition we seem to be running a fully time laundry with old style condenser drier going.

jonathanb48 wrote: ↑Sat Jan 10, 2026 10:32 am Hi great question and yes I do have intelligent octopus go but don’t know how to pick up auto battery charging when the off peak tariff cuts in during the day. If you have any guidance that would be great.

As to why we use so much power. We have a base load of 1.8kw - I know that I have 300w in my WiFi and cctv rack plus UPS and possibly some leakage from UFH pumps and in house ventilation - but working on that . In addition we seem to be running a fully time laundry with old style condenser drier going.

You would need Home Assistant to allow it to see when your Offpeak value changes in a sensor, which you can then use to program the battery to charge up.

Here is yet another video by Will, talks about Octopus Intelligent Go from around 4mins onwards, that can then change inverter mode into Force Charge.


We have a Heat Pump tumble drier, uses as low as 0.7kWh for a load, to 1.8kWh for a really big load. Maybe once your existing dies, that would be a good swap.

I do now understand you have a high base load, that will explain the high daily use.

Thanks My better half insisted on buying the last condenser drier available 3 months ago !! It uses 4kw to dry a load of clothes and I think we must be doing it for the neighbours too !

Will look at home assistant too thanks

jonathanb48 wrote: ↑Sat Jan 10, 2026 11:36 am Thanks My better half insisted on buying the last condenser drier available 3 months ago !! It uses 4kw to dry a load of clothes and I think we must be doing it for the neighbours too !

Will look at home assistant too thanks

Ouch! Well at least you know what your next tumbler dryer will be.

Home Assistant Green is a great introduction to getting it running.

And after all that managed to add another hour of charging through intelligent octopus go EV schedule and in response my inverter seemed to throttle back charging in the last hour of charging so I still only got to 92% when for another hour I should easily have got to 100% charge.Any idea why the throttle back happens

The batteries always throttle as they approach full, but usually nearer the 95% mark - have you ever done a complete charge cycle on this pack yet ?, i.e. from 10% to 100% and back to 10%.

The pack balances as it approaches 100% (see my first post above) which is why it is throttling to allow individual packs / cells the time to harmonise with the rest of the batteries - if it is starting a little earlier it suggests the batteries have not yet learnt their limits which will naturally happen after a few full charge cycles.

This forum is so helpful. Batteries have never been above 92% because inverter is too small but you can see from graph they started to throttle an hour before end of charge period which says they have learned that 92% is the max. Normally they have throttled in the last 30 mins - hope they can unlearn this !!

Is there an easy way to get them to learn 100% or am I simply going to have to go through 8 or 10 cycles edging them up. Problem I have is that I simply don’t have time for this amount of “customer commissioning”

From March onwards you'll have plenty of solar to help, these are the worst months when the majority of battery charge will come from grid.

The only way to get them to 100% is to leave them charging for as long as it takes, which at high tariff just isn't worth it.

The batteries will learn, it just takes a bit of time - they will always throttle above 95% but in summer you won't notice, for now just carry on doing what you doing and hopefully soon you'll not use all your battery during the day or we'll have a good solar day and they'll be able to charge all the way to 100%.

Ah unfortunately whilst I have solar it was put in by the developer to comply with planning and has about 2kw of capacity and does not feed my batteries as the inverter there is in a totally different part of the house- either offsets use or feeds the grid and I gather has such a low output that it probably can’t trigger a charge cycle in the batteries However that may well be something to think about as an upgrade - some proper solar but will have to look at the maths