I bought a robot mower from the internet, listed as fault but it wasn’t faulty. The battery was deeply discharged. I charged the battery separately and it checked out fine. The mower didn’t come with a charger, so I bought a compatible charger which connects to the base.
Accidently I connected it in reverse and I damaged the circuit which produces the boundary wire signal. There were two voltage regulators fried and after I replaced them the mower worked fine. I don’t have the tools or the skills to solder SMDs, so I turned to a computer repair shop to do the job for me.
I was very lucky to have the microcontroller escaped. If this one was fried, it would have been impossible to repair it, because it contains the firmware which cannot be replaced.
This model even has Bluetooth and can be controlled with the phone.
During this repair I studied the shape of the boundary wire signal from different manufacturers, and this particular one has a very complicated pattern.
So, if the base is damaged, the robot becomes impossible to use. Yes, you can charge it separately, but it doesn’t work without the boundary wire. You can try to generate some pulses, easy enough, but if you don’t know the signal pattern, then it’s game over, it’s almost impossible to guess.