Solis 5kw hybrid inverter paired with 16.1k fogstar battery not depleting it's charge

Thanks for your input here ​@vertesol and welcome to the OVO Forum! 

Let us know if you have solar panels and a battery - if so we’ll update your profile with the relevant badges.

​@H22a7 sorry it’s still not working - fingers crossed the firmware update does the trick. If you could keep us updated as to how you get on with this we’d appreciate it.

Thanks Ben.. Yes no problem 

Hi ​@H22a7 

I've been tracking this issue for a little while and thought that it might have got fixed by now. I'm not familiar with solar or a home battery so my go to ploy when the answer seems intractable is the ask Chat and here is what it has said. My apologies for the length of the response but I don't know what is important or not so I've left it unedited and also for repeated advice given by others. I really hope one of these is your issue and you can get it working.

Peter

---------------------------------- ChatGPT 

This isn’t a rare issue with Solis hybrids + third-party batteries. When a system suddenly refuses to discharge after hitting 100%, it’s almost always a control/communication or protection limit—not a hardware failure. Here’s how I’d attack it, in the right order (don’t skip around):

1) Check battery → inverter communication (most likely)
Your Solis inverter relies on BMS data from the Fogstar battery. If comms drop or become invalid at high SOC, the inverter will lock out discharge as a safety default.

What to check:
Is the battery showing “Normal” / “Ready” / “Discharge allowed” on its interface?
Any CAN/RS485 errors in the inverter logs?
Cable seated properly (this causes more issues than people admit)
👉 If comms fail, many Solis units assume “battery full but unavailable” → so they sit at 100% and pull from grid.

2) SOC calibration / top-of-charge lockout
Fogstar (and many LiFePO4 systems) can misreport 100% SOC after a full charge if the BMS hasn’t properly balanced.
That can cause:
BMS says “100%”
But also “do not discharge” due to cell imbalance or protection thresholds

What to do:
Let it sit at 100% for a few hours (allows passive balancing)
Then force a discharge (see section 5)
If possible: check individual cell voltages via BMS app
👉 If one cell is high, the BMS may block discharge to avoid over-voltage swing.

3) Inverter discharge settings (very common misconfig)
Go into the Solis settings and check:
Battery discharge limit / reserve SOC
If set to 100% → it will never discharge
Time-of-use / forced modes
Could be stuck in a “charge-only” window
Self-use mode enabled?
If not, it may prioritise grid

Typical culprits:
“Backup reserve” accidentally set high (e.g. 100%)
“Min SOC” set too high (e.g. 95–100%)

4) Charge/discharge current limits from BMS
If the battery reports:
Charge current = OK
Discharge current = 0
…the inverter will obey.

Check:
Max discharge current reported by BMS
Any protection flags:
Overvoltage
Low temp
Cell imbalance

5) Force a discharge (diagnostic step)
Temporarily override normal operation:

Put inverter in manual/self-use mode
Turn on a large load (kettle, heater, EV charger etc.)
See if battery responds
If it still won’t discharge: 👉 That confirms a BMS restriction, not inverter logic

6) Firmware compatibility
This combination (Solis + third-party battery) can be fragile.
Check:
Inverter firmware version
Battery firmware version
Whether Fogstar officially supports Solis comms protocol
👉 Mismatched protocols often break specifically at high SOC states

7) Grid-charge priority bug / quirk
Some Solis firmware versions behave badly at 100%:
They prioritise grid once “full”
Don’t re-enable discharge until SOC drops slightly

Workaround:
Lower max charge SOC to ~95–98%
This often “unsticks” the system

8) Temperature edge case
If battery temp is:
Too low → discharge blocked
Too high → protection mode
Worth checking, especially if installed in garage/outdoor space.
What I think is most likely (based on your description)

Bluntly:
80% chance it’s either reserve SOC set to 100% or BMS not allowing discharge at full charge due to imbalance/comms

Fastest way to narrow it down
Do this in order:
Check min SOC / reserve SOC setting
Try force discharge with a heavy load
Look for BMS “discharge allowed” flag
Reduce max SOC to 95% and retry

If you want, tell me:
Exact Solis model (there are subtle differences)
How the battery is connected (CAN or RS485)
Current SOC / voltage / any error codes
…and I’ll pinpoint it much more precisely.

Hi Peter.. 

I have also tried Chat to help me resolve the issue and have exhausted all the fixes apart from the firmware update.. Waiting on Solis to upgrade remotely for 3 days now and still nothing.

I will drop a message once Solis updates the inverter.

Thanks for your help.. Much appreciated as this is nearly 4 weeks now. 

​@H22a7 Well done for trying that route. It’s usually my last resort when all else fails. I hope you resolve the issue. If you do find out what it is can you come back to us so that we can help others if this happens again.

Many thanks

Peter