FoxESS Community - Owners & Installers Forum

Hi all,

I'm an absolute novice when it come to this but 2 years ago I had 10solar panels a fox ess inverter and 2 HV2600 2.6kw batteries.

We are getting our ASHP installed next month and I'm looking to increase the battery capacity so we can store more power overnight in the cheap charging period. (Using octopus flux). I have been quoted £2400 to install 2 more batteries from the company that installed my original system but have seen on the eco supermarket that batteries are only about £700 so I could be in line to save £1000 by installing myself.

I suppose what I'm looking for is guidance on how I identify which exact battery, versions and so on, I will need to buy and and advice on how to actually install them myself? (Don't want to get electrocuted in the loft) .

Thanks very much and sorry if this has been explained before I've had a browse through and can't find an answer in the most simple layman's terms that I'm after.

Steve

Hi Steve,

If your HV2600 batteries are 2 years old it is very likely they are V1 batteries - you would normally expect to see a white sticker on the front saying Ver:C or Ver:D

If they are V1 batteries they are rare as hens teeth to find them (you might find them on eBay), but there is a V2 HV2600 battery available which is what you are seeing on-line however they need the V1 BMS unit replacing for a V2 BMS to work with your V1 batteries so that will have to be priced in (~£200).

When you mix the V1 & V2 battery types as your V1’s are 2 years old because of ageing they may limit the pack and the amount of power the new batteries can provide to perhaps 90% of what you would expect if all were new.

In addition to Dave's correct and accurate advice I wanted to give a fresh idea.

As you only have 2 x HV2600 and they're rare and easy to sell, why not sell them and install a brand new stack of ECS cubes? Keep the same inverter and all the wiring, just replace the batteries.
ECS cubes start at 6kWH and scale to over 41kWH.

Thanks very much for the detailed information.

I've just had a reply from Ollie at eco supermarket, I sent a screenshot of my batteries from the app and he said they are version 2 so should be good to add 2 additional ones on. I must have been fairly lucky maybe one of the early people to get the version 2's?

The ECS cube things look good but I think on account of getting lucky (I will double check when I get home to see what sticker they have, what sticker indicates a version 2) I will just add more of these HV2600.

I have seen some videos on YouTube, is it really as simple as just adding them to the stack and connecting the 4 cables, earth data and the red and black ones?

Thanks again for all the information.

Correct, discharge to 50%, isolate battery stack and inverter and turn it all off.
Remove data and earth from BMS. Unplug the HV leads from the first battery, lift off the bms and place to the side.
Carefully add the batteries, make sure you don't accidently short circuit the batteries. Always make sure the final connections go to the bms again not to the top battery as you'll short them out and blow fuses.
Increment the BMS dip switch one click/number for each extra battery. Note that the number is 2 less than the real battery count.
Turn it all on and try to do some full cycle charges and discharges allowing anything from days to weeks for it to all balance.

Hi I've just done exactly this i.e. adding 5 more FoxCube batteries from EcoSupermarket and it was really quite easy. The only fiddly bit was the clips on the battery terminals. I'll post some pictures I took of how to do this. There are some on the forum already but as usual its easy once you've done it once, a bit difficult to know which bit to push until then despite the instructions. It all seems to be OK with the apps seeing installed battery capacity etc but I was naughty and as it was super sunny I added the new batteries when the existing one slave and Master were at 100% rather than 50% Will it sort itself out after a few charge/discharge cycles or should I start again from 50%? Any advice appreciated. Thanks!

browgars wrote: Thu Feb 06, 2025 5:01 pm I added the new batteries when the existing one slave and Master were at 100% rather than 50% Will it sort itself out after a few charge/discharge cycles or should I start again from 50%? Any advice appreciated. Thanks!

That’s a really big difference, and even with full charge / discharge cycles it’s likely to take 2 or 3 weeks (or more) before they start to balance out properly - and in the meantime the smaller full batteries will limit the pack capacity. It might be easier to temporarily take it back to 2 batteries - discharge them hard so they are nearer 50% and then re-connect the new batteries.

Don’t forget to ask your installer (or Fox) to update the firmware so they are all running the same version.

Thanks - I'll try that. Cheers

Hello all,

looking todo a similar thing. I would like to know the impact on the MCS certificate? In theory it would not be an MCS approved system anymore and therefore in theory any provide could refuse to pay for export? Does anyone have any views on this point?

Just had a look at my MCS certificate, it actually only covers the PV install, including inverter and wiring and all isolators. The certificate itself does not mention the battery or its size. Still keen to hear other opinions on this, as there are significant savings possible.

Update from my end. I did as Will suggested and removed the 5 extra batteries. Charged those to 50% and then added the 5 new cubes. Seemed to sort itself out quickly after that and I’m getting nearly 20kWh storage on sunny days. Before removing the extras I only got just over the original storage. Moral of that story RTFM Thanks for all the help