FoxESS Community - Owners & Installers Forum

I had a Fox system installed last month (7 panels, 2xEP11 batteries and a 5kW H1 hybrid inverter). I've also got a Zappi EV charger.

Despite quite a bit of sunshine today, my battery has been stuck charging at 99% for about four hours. It has previously got up to 100% several times no problem, seemingly without delay, and then exported the excess solar. I understand there are things that slow charging when nearly full to preserve battery life (top-balancing?), but where does that extra energy go? Is it stored in the battery and available when it discharges? Or would it be better to set the max SOC to 99% (or lower?) so it will stop trying to charge the last little bit and instead export the solar? (Or in the case of a forced charge, to just stop importing from the grid.)

Of course, within five minutes of posting this, it has just got to 100% and is now exporting the tiny bit of extra solar still around...

The BMS does quite a few things in the last few % as it approaches 100 where it starts to throttle the charge and allow a slower top balance.

A few things to note, the inverter places a small drain on the battery to keep it up and running, you tend not to notice it when PV is generating but at night time you may notice a constant small drain - typically between 30-100 watts depending on the inverter size.

When the battery gets to 100% the BMS holds any further battery charge - it does this to maintain life, reduce stress / heat and continuous cycling and it remains like that typically until the battery falls back to 97% (or the cell volts settle and it decides to allow charge again) - that might take some time particularly when you have PV generation as the inverter drain as already mentioned is small.

So all that said it’s not unusual to see the battery in the 97-99% range during the day and not charging, any excess PV is always exported.