Apparent very low battery temperature

I have 2 x 8.2kWh batteries installed. On 13/06/23 I noticed that when the batteries were charging the percentage charge fluctuated to 65 - 70% to regardless of the state of charge. I also noticed on the same day that in the afternoon when the battery should have been utilising all the solar generated power it was only charging at about 1250W as opposed to 2850W. The excess solar power was being exported. I updated the software and recalibrated the system. The following day I noticed that when the battery was charging following the recalibration discharge the battery percentage wasn’t registering. I called Givenegy support and they reset the inverter again. This didn’t cure the problem and the battery percentage fluctuation happened again whilst the battery was recharging during the morning of 18/06/23 (this morning).

Using the Cloud, I have gone back over the data and find that the first occurrence was on 21/05/23. I also find that apart from the 13/06/23 where the anomaly lasted for 4 hours, the percentage charge and associated drop in charging power only fluctuates for 1 data point before returning to the previous (true) reading, however this can repeat, often every 15 minutes or so. This morning during a seven hour charge it happened 16 times. I have also found that the fluctuation coincides with the recorded battery temperature dropping from normal to -75C! Obviously the temperature doesn’t drop to -75C but this seems to be the cause of the charging cycle disruption.

Any ideas anybody?

I would ask your installer to check the communication cables between the batteries and inverter. Erratic temperature readings and odd charing rates could be a sign of poor comms connection (inverter can't read state of battery or its sensors). I assume you have attempted an inverter and battery restart. I await other more experienced replies/advice but that's where I'd start.

I had an issue with bizarre temperature readings from my (externally fitted) battery. The installer had bent the comms cable at a tight angle and moisture had found the weak point. A new cable at a less severe bend solved the issue.