Battery not charging to 100% overnight

Does anyone have any ideas why my battery (9.5 plus AC Coupled Inverter) stopped charging significantly at around 2:30 last night. It reached about 78% before 4:30.

I’m on Octopus Go and my app settings are below:

The inverter temperature was about 46C. Battery temp was steady at 26C and grid voltage about 242-244V.

It’s happened a couple of times now, and while only a minor annoyance, it’s frustrating that it won’t see us through the day now given the weather.

Spoke to GE support and they believe there is a problem with one of the cells. They are doing a calibration at trickle charge speeds (could take 18 hours), and if it doesn't fix it, they will replace the battery, which has had various problems from day one.

As an aside they answered the phone almost immediately, which is a great improvement on the previous wait times.