My robot cleaner stopped charging after a week of not being used. I gave the same error as when I removed the battery. I then measured the voltage across the battery terminals, which is 0.01VDC.
I then pried open the case and measured the voltage across each battery, which is 4 VDC, so the batteries seem OK.
So I suspected the circuit is malfunctioning, and when I search for help, all I can find is how to revive dead batteries, nothing about the circuit.
Any tips on attempts to troubleshoot this or determine if the circuit is dead? It would be a shame trash the entire device its fixable.