Ok, I have now used the inverter coupled to both the controller load output and direct to the battery.
In both cases the charge controller does the following:
does not charge the battery beyond 12.1v
when the battery drops below 11.3v the charge controller goes into undervoltage mode and stops charging. It does not 'come out' of undervoltage mode- it will not charge the battery back from whatever voltage the battery has dropped to under any lighting condition. I have to turn the unit off and back on again.
I have looked at the instructions that were provided with the kit and the stats do not reflect either situation.
The battery I am using is this: https://batterygroup.co.uk/batteries-by-type/agm-batteries/13306/q-batteries-12lcp-15/12v-15ah-lead-battery-cycle-type-agm-deep-cycle-vrla-screw-connection-m5#gref
Edit:
Well I may have read the voltage at the wrong time because today it does go under voltage at 10.6v which IS stated in the manual. It bounces back to 11.3v when the load is removed.
I'm still not sure what to do about the undervoltage reset. I think I might leave it like that all day and see what happens.
So I have left the unit in 'undercharge' mode. It has reset itself to 'normal' mode, the load function is operative again and the battery has now recharged to 12.2v.
To be fair this is the first day since I bought the kit that we've had enough sunlight to operate the contoller effectively.
While it doesnt specify precicely the operation of the controller in the instructions it does do what I'd expect a controller to do.
I suspect though, that once the load function has tripped out due to undervoltage you will have to re-engage it. That also wants testing.