Charging issues

I think it's more likely to be a battery issue or a firmware issue. On the odd occasion it charges fully and I set it to clean it is returning back to the dock to charge after 30 minutes if it makes it back. It then can charge and come back out in an hour and finish off or for instance yesterday it went back to charge around 7 last night and didnt come back out to finish the job until 11 am this morning!