I have a 12 x 450W solar array coupled to a Foxess H1-5.0-E-G2-WL inverter with and attached EP12 battery - the battery version_BMS is 1.011, the inverter version_Master is 1.47, version_Slave is 1.04 and version_ARM is 1.35. The data logger is WL-H1-WL with software version 2.06.
The system was installed on 19th November 2025 and seems to work fine with, what seem to be to me a notable anomaly - the system seems unable to regard Reserve State of Charge as an immovable barrier in that the SoC sometimes decreases below it with no attempt by the system to top it up from the grid. The other thing is the there SoC seems to have a mind of its own - increasing or decreasing by 1% with not evident reason that I can see, i.e. not taking power from the grid when it increases (with no input from PV being evident - e.g. at night) and not generating power when it decreases.
What is going on? I have pictures of this if it helps.
Probably best to start by saying a battery is an electro chemical device that is affected by temperature changes which probably explains small % changes, better to think of it as a fuel gauge rather than a totally accurate %, if it’s jumping by 20% then it’s time to worry.
There are plenty of posts on here about LFP batteries, but to keep it short they have a very flat voltage from nearly full to nearly empty, and an EP12 battery has a considerable number of cells within it that have to establish balance.
Balancing occurs when the battery approaches 100% and 10% where the cell voltages rise and drop rapidly and so the battery has to be fully charged and discharged several times before all the cells have had the chance to balance and the battery manager establishes what constitutes the limits. The battery manager constructs the SoC or battery reserve it presents to you from all of the cell voltages within it, and so even being sat on a cold concrete floor or against a wall can affect the individual cells slightly.
The inverter always takes a small amount of power from the batteries (or PV when present) and whilst only a small drain, over time it will discharge the battery, and your batteries are supporting the house load when there is no PV present.
It’s good practice to fully charge cycle the battery at least once a month to maintain that balance, have you done any full charges on the system from grid, or you relying on what little solar is available at this time of year ?
There are plenty of posts on here about LFP batteries, but to keep it short they have a very flat voltage from nearly full to nearly empty, and an EP12 battery has a considerable number of cells within it that have to establish balance.
Balancing occurs when the battery approaches 100% and 10% where the cell voltages rise and drop rapidly and so the battery has to be fully charged and discharged several times before all the cells have had the chance to balance and the battery manager establishes what constitutes the limits. The battery manager constructs the SoC or battery reserve it presents to you from all of the cell voltages within it, and so even being sat on a cold concrete floor or against a wall can affect the individual cells slightly.
The inverter always takes a small amount of power from the batteries (or PV when present) and whilst only a small drain, over time it will discharge the battery, and your batteries are supporting the house load when there is no PV present.
It’s good practice to fully charge cycle the battery at least once a month to maintain that balance, have you done any full charges on the system from grid, or you relying on what little solar is available at this time of year ?
It arrived on 19/11 with 50% charge in it which the BMS then gradually discharged down to the 10% indicated bottom limit.
The 20th was a so so solar day, but the PV charged the battery up to 29% indicated.
On the 21st I tried out the function which allowed the battery to charge from the grid overnight, that took it to 94% indicated - I didn't stop it at that value, I was fast asleep.
By about 10am on the 22nd it had decreased to 78% indicated due to house load and then, because it was a reasonable solar day charged up to 100% 13:23. At this point I set the reserve SoC to 50% having in mind that having a good state of charge on a new battery might be a good idea, however, on the 23rd I set the reserve SoC to 20% thinking it was not a good idea to let it drop all the way to 10%. So far so good, I hadn't noticed any of the 1% changes up to then. But on the 24th the 1% drops appeared - two of them spaced hours apart took the SoC down 18% (the battery warming function was still disabled then), the battery temperature was around 9C and it was not a good solar day.
The 25th was a nice day, the SoC got to 75% indicated.
The 26th was an even better day, the SoC got to 96% indicated.
The 27th finished at 27% indicated.
The 28th got to 62% indicated.
I've also tried lowering the reserve to 15% and now returned it to 20%, but currently, due to the 1% changes it's down to 16%.
I have seen it decide to draw from the grid to top up the battery but the SoC value seems not to be factor which causes its internal algorithms to make that decision.
I have a technological background in computers and comms, but nil in solar, inverters and LP batteries, so maybe I'm just worried well and very curious about wtf is going on.
Any help is greatly appreciated.
Best regards and thanks so far
Derrick.
The 20th was a so so solar day, but the PV charged the battery up to 29% indicated.
On the 21st I tried out the function which allowed the battery to charge from the grid overnight, that took it to 94% indicated - I didn't stop it at that value, I was fast asleep.
By about 10am on the 22nd it had decreased to 78% indicated due to house load and then, because it was a reasonable solar day charged up to 100% 13:23. At this point I set the reserve SoC to 50% having in mind that having a good state of charge on a new battery might be a good idea, however, on the 23rd I set the reserve SoC to 20% thinking it was not a good idea to let it drop all the way to 10%. So far so good, I hadn't noticed any of the 1% changes up to then. But on the 24th the 1% drops appeared - two of them spaced hours apart took the SoC down 18% (the battery warming function was still disabled then), the battery temperature was around 9C and it was not a good solar day.
The 25th was a nice day, the SoC got to 75% indicated.
The 26th was an even better day, the SoC got to 96% indicated.
The 27th finished at 27% indicated.
The 28th got to 62% indicated.
I've also tried lowering the reserve to 15% and now returned it to 20%, but currently, due to the 1% changes it's down to 16%.
I have seen it decide to draw from the grid to top up the battery but the SoC value seems not to be factor which causes its internal algorithms to make that decision.
I have a technological background in computers and comms, but nil in solar, inverters and LP batteries, so maybe I'm just worried well and very curious about wtf is going on.
Any help is greatly appreciated.
Best regards and thanks so far
Derrick.