I have an Ozmo Deebot 900 Robot Vacuum Cleaner (purchased from Aldi).
I have found that if the vacuum cleaner is turned off at the mains the night before (after being fully charged), that the next morning it will be flat, and take a few hours to recharge.
I went to lodge a warranty claim with the manufacturer, and they have told me this is how they are designed.
It sounds a little suspicious to me, as I would expect the battery to retain charge (similar to any other chargeable battery device).
Any owners able to confirm that this is normal behavior for the vac?
My Xiaomi robot vacuum cleaner goes flat after a while if you turn off the charging dock. I am guessing it uses charge to be constantly connected to wifi, even when it is not doing any vacuuming. Did you expect the wifi-connected vacuum cleaner to turn off completely after it finish charging?